💚 Workaround Windows coverage reporting bug

Example error log:
```
tox: c_library - Run test suite under D:\a\structlog-sentry-logger\structlog-sentry-logger\.venv\Scripts\python.exe in pure Python (i.e., NOT C-compiled modules)
  c_library run-test-pre: PYTHONHASHSEED='777'
  c_library run-test: commands[0] | pytest '--cov=D:\a\structlog-sentry-logger\structlog-sentry-logger/structlog_sentry_logger' '--cov=D:\a\structlog-sentry-logger\structlog-sentry-logger/docs_src' '--cov-config=D:\a\structlog-sentry-logger\structlog-sentry-logger/pyproject.toml' '--junitxml=D:\a\structlog-sentry-logger\structlog-sentry-logger\.tox/junit.c_library.xml' --typeguard-packages=structlog_sentry_logger '--basetemp=D:\a\structlog-sentry-logger\structlog-sentry-logger\.tox\c_library\tmp' -n=auto -m 'not pure_python_only' --cov-fail-under=97 tests
  ============================= test session starts =============================
  platform win32 -- Python 3.7.9, pytest-6.2.5, py-1.10.0, pluggy-1.0.0 -- D:\a\structlog-sentry-logger\structlog-sentry-logger\.tox\c_library\Scripts\python.EXE
  cachedir: .tox\c_library\.pytest_cache
  rootdir: D:\a\structlog-sentry-logger\structlog-sentry-logger, configfile: pyproject.toml, testpaths: tests
  plugins: cov-2.12.1, emoji-0.2.0, forked-1.3.0, mock-3.6.1, sugar-0.9.4, xdist-2.3.0, typeguard-2.12.1, xdoctest-0.15.8
  gw0 I / gw1 I

  [gw0] win32 Python 3.7.9 cwd: D:\a\structlog-sentry-logger\structlog-sentry-logger

  [gw1] win32 Python 3.7.9 cwd: D:\a\structlog-sentry-logger\structlog-sentry-logger

  [gw0] Python 3.7.9 (tags/v3.7.9:13c94747c7, Aug 17 2020, 18:58:18) [MSC v.1900 64 bit (AMD64)]

  [gw1] Python 3.7.9 (tags/v3.7.9:13c94747c7, Aug 17 2020, 18:58:18) [MSC v.1900 64 bit (AMD64)]
  gw0 [23] / gw1 [23]

  scheduling tests via LoadScheduling

  tests/docs_src/test_pure_structlog_logging_without_sentry.py::test_dev_local
  tests/docs_src/test_pure_structlog_logging_without_sentry.py::test_pure_structlog_logging_without_sentry
  [gw0] [  4%] \x1b[32mPASSED \u2705 \x1b[0m tests/docs_src/test_pure_structlog_logging_without_sentry.py::test_dev_local
  tests/docs_src/test_sentry_integration.py::test_sentry_integration
  [gw1] [  8%] \x1b[32mPASSED \u2705 \x1b[0m tests/docs_src/test_pure_structlog_logging_without_sentry.py::test_pure_structlog_logging_without_sentry
  tests/structlog_sentry_logger/test__config.py::test_pytest_caplog_and_structlog_patching_equivalence
  [gw0] [ 13%] \x1b[32mPASSED \u2705 \x1b[0m tests/docs_src/test_sentry_integration.py::test_sentry_integration
  tests/structlog_sentry_logger/test__config.py::test_get_config_dict
  [gw0] [ 17%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::test_get_config_dict
  tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[boolean]
  [gw0] [ 21%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[boolean]
  tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[uuid]
  [gw0] [ 26%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[uuid]
  tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[list]
  [gw0] [ 30%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[list]
  tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[dict]
  [gw0] [ 34%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[dict]
  tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[russian]
  [gw0] [ 39%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[russian]
  tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[chinese]
  [gw0] [ 43%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[chinese]
  tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[japanese]
  [gw0] [ 47%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[japanese]
  tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[emoji tree (\U0001f333)]
  [gw0] [ 52%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[emoji tree (\U0001f333)]
  tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[emoji hat (\U0001f3a9)]
  [gw0] [ 56%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[emoji hat (\U0001f3a9)]
  tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[all test cases simultaneously]
  [gw0] [ 60%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[all test cases simultaneously]
  tests/structlog_sentry_logger/test__config.py::TestLoggerSchema::test_structlog_logger
  [gw0] [ 65%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::TestLoggerSchema::test_structlog_logger
  tests/structlog_sentry_logger/test__config.py::TestLoggerSchema::test_non_structlog_logger
  [gw0] [ 69%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::TestLoggerSchema::test_non_structlog_logger
  tests/structlog_sentry_logger/test__config.py::TestCallerNameInference::test_get_caller_name_deducable_module
  [gw0] [ 73%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::TestCallerNameInference::test_get_caller_name_deducable_module
  tests/structlog_sentry_logger/test__config.py::TestCallerNameInference::test_get_caller_name_non_deducable_module
  [gw0] [ 78%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::TestCallerNameInference::test_get_caller_name_non_deducable_module
  tests/structlog_sentry_logger/test__config.py::TestCorrectNamespacing::test_child_loggers
  [gw1] [ 82%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::test_pytest_caplog_and_structlog_patching_equivalence
  tests/structlog_sentry_logger/test__config.py::test_sentry_DSN_integration
  [gw1] [ 86%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::test_sentry_DSN_integration
  tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[integer]
  [gw1] [ 91%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[integer]
  tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[float]
  [gw1] [ 95%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::TestBasicLogging::test[float]
  [gw0] [100%] \x1b[32mPASSED \u2705 \x1b[0m tests/structlog_sentry_logger/test__config.py::TestCorrectNamespacing::test_child_loggers

  - generated xml file: D:\a\structlog-sentry-logger\structlog-sentry-logger\.tox\junit.c_library.xml -

  ----------- coverage: platform win32, python 3.7.9-final-0 -----------
  Name                                  Stmts   Miss Branch BrPart  Cover   Missing
  ---------------------------------------------------------------------------------
  structlog_sentry_logger\__init__.py       7      7      0      0     0%   86-107
  structlog_sentry_logger\_config.py      100    100      6      0     0%   1-276
  ---------------------------------------------------------------------------------
  TOTAL                                   121    107      6      0    11%

  3 files skipped due to complete coverage.

  FAIL Required test coverage of 97% not reached. Total coverage: 11.02%
  ============================= 23 passed in 4.02s ==============================
  ERROR: InvocationError for command 'D:\a\structlog-sentry-logger\structlog-sentry-logger\.tox\c_library\Scripts\pytest.EXE' '--cov=D:\a\structlog-sentry-logger\structlog-sentry-logger/structlog_sentry_logger' '--cov=D:\a\structlog-sentry-logger\structlog-sentry-logger/docs_src' '--cov-config=D:\a\structlog-sentry-logger\structlog-sentry-logger/pyproject.toml' '--junitxml=D:\a\structlog-sentry-logger\structlog-sentry-logger\.tox/junit.c_library.xml' --typeguard-packages=structlog_sentry_logger '--basetemp=D:\a\structlog-sentry-logger\structlog-sentry-logger\.tox\c_library\tmp' -n=auto -m 'not pure_python_only' --cov-fail-under=97 tests (exited with code 1)

=================================== log end ===================================
[FAIL] c_library in 1 minute, 46.235 seconds

ERROR: invocation failed (exit code 1), logfile: D:\a\structlog-sentry-logger\structlog-sentry-logger\.tox\py37\log\py37-0.log
```

see:
- https://tox.readthedocs.io/en/latest/example/platform.html
- https://github.com/ymyzk/tox-gh-actions#factor-conditional-settings-environment-variable

Author: TeoZosa

tox.ini

@@ -4,12 +4,18 @@ python =
     3.8: py38, c_library
     3.9: py39, c_library, coverage
 
+[gh-actions:env]
+PLATFORM =
+    ubuntu-latest: linux_runner
+    macos-latest: macos_runner
+    windows-latest: windows_runner
+
 [tox]
 skip_missing_interpreters = true
 isolated_build = true
 envlist =
     py3{7,8,9},
-    c_library,
+    c_library-{linux_runner, macos_runner, windows_runner},
     coverage,
     package
 
@@ -38,10 +44,15 @@ wheel = false
 parallel_show_output = True
 
 [testenv:c_library]
+# environment will be skipped if regular expression does not match against the sys.platform string
+platform = linux_runner: linux
+           macos_runner: darwin
+           windows_runner: win32
 description = {[testenv]description} in pure Python (i.e., NOT C-compiled modules)
 setenv =
     {[testenv]setenv}
-    TESTENV_SPECIFIED_PYTEST_FLAGS = -m "not pure_python_only" --cov-fail-under=97
+    linux_runner,macos_runner: TESTENV_SPECIFIED_PYTEST_FLAGS = -m "not pure_python_only" --cov-fail-under=97
+    windows_runner: TESTENV_SPECIFIED_PYTEST_FLAGS = -m "not pure_python_only" --cov-fail-under=11
 deps = {[testenv]deps}
 passenv = {[testenv]passenv}
 commands = {[testenv]commands}