add 3.12 to cron runners

[IAlibay]

Fixes #

Changes made in this Pull Request:

PR Checklist

• Tests?
• Docs?
• CHANGELOG updated?
• Issue raised/referenced?

Developers certificate of origin

• I certify that this contribution is covered by the LGPLv2.1+ license as defined in our LICENSE and adheres to the Developer Certificate of Origin.

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📚 Documentation preview 📚: https://mdanalysis--4443.org.readthedocs.build/en/4443/

[github-actions]

Linter Bot Results:

Hi @IAlibay! Thanks for making this PR. We linted your code and found the following:

There are currently no issues detected! 🎉

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (5a992d7) 93.37% compared to head (e2e753b) 93.38%.

Additional details and impacted files

@@            Coverage Diff             @@
##           develop    #4443     +/-   ##
==========================================
  Coverage    93.37%   93.38%             
==========================================
  Files          171      185     +14     
  Lines        21737    22851   +1114     
  Branches      4012     4012             
==========================================
+ Hits         20298    21339   +1041     
- Misses         952     1025     +73     
  Partials       487      487             

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[RMeli]

LGTM, thanks @IAlibay