Update test CI to use Python 3.12

[byrdie]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.51%. Comparing base (23dd8b3) to head (3e14156).
Report is 12 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main       #6   +/-   ##
=======================================
  Coverage   98.51%   98.51%           
=======================================
  Files           3        3           
  Lines         202      202           
=======================================
  Hits          199      199           
  Misses          3        3           

Flag	Coverage Δ
unittests	98.51% <ø> (ø)

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