fix(marks): reject unknown kwargs in skip/skipif (#14839)

[Carltonkenny]

Summary

Fix pytest#14839: pytest.mark.skipif(strict=True, reason=...) and pytest.mark.skip(strict=True, reason=...) are silently accepted instead of raising a clear error.

In a pytest training, a participant mistakenly added strict=True to a skipif marker in a file instead of the xfail one, and was surprised that nothing happened.

Before

import pytest

@pytest.mark.skipif(True, strict=True, reason="")
def test_x():
    pass   # silently accepted; the strict=True is stored on the mark
           # and ignored at apply time.

After

>>> pytest.mark.skipif(True, strict=True, reason="")
TypeError: pytest.mark.skipif() got unexpected keyword argument(s): strict. Allowed: reason.

Implementation

Added a per-builtin-mark kwarg allow-list (skip: {reason}, skipif: {reason},
xfail: {condition, reason, run, raises, strict}) validated in
MarkDecorator.with_args. Custom (user-registered) marks are not validated
because we cannot know their parameter schema.

Tests

• 6 new regression tests in TestBuiltinMarkKwargsValidation.
• All 117 pre-existing mark tests still pass (123 total now).

Fixes #14839.

[RonnyPfannschmidt]

clank