Sync .flake8 with template

We have assembled a collection of reusable project assets:
https://github.com/arduino/tooling-project-assets
These will be used in the repositories of all Arduino tooling projects.

This change only provides a sync with the upstream asset and has no functional effect.

Author: per1234

Diff for: .flake8

@@ -1,9 +1,12 @@
+# Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/assets/check-python/.flake8
+# See: https://flake8.pycqa.org/en/latest/user/configuration.html
+# The code style defined in this file is the official standardized style to be used in all Arduino tooling projects and
+# should not be modified.
+
 [flake8]
 doctests = True
-ignore =
-    # W503 and W504 are mutually exclusive, so one or the other must be ignored.
-    # PEP 8 recommends line break before, so we keep W504.
-    W503
+# W503 and W504 are mutually exclusive. PEP 8 recommends line break before.
+ignore = W503
 max-complexity = 10
 max-line-length = 120
 select = E,W,F,C,N