GitHub Actions: Test on Python 3.14 release candidate 2

[cclauss]

Python v3.14 -- October 7th

• https://www.python.org/download/pre-releases
• https://www.python.org/downloads/release/python-3140rc2

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.18%. Comparing base (a3fa581) to head (fbddb4c).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #945   +/-   ##
=======================================
  Coverage   88.18%   88.18%           
=======================================
  Files          32       32           
  Lines        1007     1007           
  Branches      105      105           
=======================================
  Hits          888      888           
  Misses        101      101           
  Partials       18       18           

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