gh-140922: Document fnmatch.translate \Z to \z change in 3.14

[kovan]

Summary

• Adds versionchanged:: 3.14 note to fnmatch.translate() documentation
• Explains that the generated regular expression now uses \z instead of \Z
• Notes that both are equivalent and \Z is still accepted for compatibility

Source verification

• Verified in Lib/fnmatch.py:188 that \z is used
• Commit add0ca9ea00 made this change

Test plan

• make check passed

🤖 Generated with Claude Code

• Issue: fnmatch.translate changed in an undocumented way in Python 3.14 #140922

---

📚 Documentation preview 📚: https://cpython-previews--144457.org.readthedocs.build/

[picnixz]

Please, always read the issue description and its corresponding thread. The indication should have gone first into "Porting to 3.14" notes as this one is an implementation detail, though I think it's also fine to have it as a "versionchanged".

cc @serhiy-storchaka

[bedevere-app]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.