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

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📚 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]

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[serhiy-storchaka]

There were no versionchanged for past changes, so I do not think it is worth to add it for this one.

An alternative is to simply restore \Z.

[picnixz]

Ok, let's just close this and keep it as an implementation detail. Strictly speaking, users shouldn't really play with the generated regex, or if they want to play with it, they should be careful. We can still discuss whether we restore \Z or not, but that could be an issue as we are quite a few releases in 3.14 (and thus some people may have already changed their code).