fix: validate keyword arguments for pytest.mark.skipif (#14839)

[The-habib]

Summary

This PR adds keyword argument validation for pytest.mark.skipif. Previously, any unsupported keyword argument passed to @pytest.mark.skipif (such as strict=True) was silently ignored. Now, evaluate_skip_marks validates keyword arguments and raises a TypeError when unexpected arguments are passed (including a helpful hint when strict is passed).

Closes #14839

Problem

When a user mistakenly writes @pytest.mark.skipif(True, strict=True, reason="") instead of pytest.mark.xfail, pytest.mark.skipif silently ignores strict=True. In contrast, pytest.mark.skip validates its arguments.

Solution

In src/_pytest/skipping.py (evaluate_skip_marks), validate that mark.kwargs only contains "condition" and "reason". If unexpected keyword arguments are present, raise a TypeError. If strict is passed, append a helpful hint - maybe you meant pytest.mark.xfail?.

Testing

• Updated existing test_marked_one_arg_with_reason in testing/test_skipping.py.
• Added unit tests test_marked_skipif_unexpected_kwarg and test_marked_skipif_strict_kwarg in testing/test_skipping.py.
• Verified all tests in testing/test_skipping.py and testing/test_mark.py pass.
• Added news fragment changelog/14839.bugfix.rst.
• Added entry to AUTHORS.