[pydocstyle] Document fix safety (D400)

[Joosboy]

Addresses #15584 for D400. Adds fix safety documentation to the D400 rule.

[astral-sh-bot]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[ntBre]

Thanks! I just updated the summary to remove the closing keyword. #15584 is a tracking issue, so we can't close it until all of the rules are covered.