CI: test on Python 3.13

[mj-will]

Include Python 3.13 in the CI.

This will probably break things!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.89%. Comparing base (e9ea69b) to head (0303500).
Report is 8 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #431   +/-   ##
=======================================
  Coverage   93.89%   93.89%           
=======================================
  Files          72       72           
  Lines        7027     7027           
=======================================
  Hits         6598     6598           
  Misses        429      429           

Flag	Coverage Δ
unittests	93.89% <ø> (ø)

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[mj-will]

Since we use conda, we'll need to wait for Python 3.13. to be released on conda-forge