[shoka-jp]

Add a Windows-specific filterwarnings example using pytest_collection_modifyitems and item.add_marker(). This lets users ignore a known warning on one platform while retaining their existing warning policy elsewhere. The text also explains that collection-time import warnings are outside the example's scope.

Related to #7525; this documents an existing workaround and does not add environment-marker syntax to configuration files.

Validation:

• Executed the snippet extracted from the documentation with Python 3.11.8, pytest 9.2.0 and filterwarnings = error. The matching-platform case ignored the known warning while an unrelated warning still failed; the nonmatching case failed on both warnings as expected.
• Full Sphinx HTML build passed with -W --keep-going.
• git diff --check passed.

Prepared with Codex assistance under human direction; AI attribution is included in the commit trailer.

• Allow maintainers to push and squash when merging my commits.
• AI agent credited in Co-authored-by commit trailer.