Declare support for Python 3.12

[hugovk]

Python 3.12 is now in beta, let's declare support.

• https://peps.python.org/pep-0693/
• https://discuss.python.org/t/python-3-12-beta-1-and-feature-freeze-is-here/26982?u=hugovk
• https://dev.to/hugovk/help-test-python-312-beta-1508

[codecov]

Codecov Report

Merging #119 (8619d27) into main (039418e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #119   +/-   ##
=======================================
  Coverage   99.06%   99.06%           
=======================================
  Files           9        9           
  Lines         745      745           
=======================================
  Hits          738      738           
  Misses          7        7           

Flag	Coverage Δ
macos-latest	97.85% <ø> (ø)
ubuntu-latest	97.85% <ø> (ø)
windows-latest	95.97% <ø> (ø)

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