bpo-34272: Reorganize C API tests. (pythonGH-8551)

Move some C API tests into Lib/test/test_capi/.

Author: serhiy-storchaka

Lib/test/test_capi/__init__.py

@@ -0,0 +1,5 @@
+import os
+from test.support import load_package_tests
+
+def load_tests(*args):
+    return load_package_tests(os.path.dirname(__file__), *args)

Lib/test/test_capi/__main__.py

@@ -0,0 +1,3 @@
+import unittest
+
+unittest.main('test.test_capi')

Lib/test/test_getargs2.py renamed to Lib/test/test_capi/test_getargs.py

@@ -0,0 +1 @@
+Some C API tests were moved into the new Lib/test/test_capi/ directory.