Declare support for Python 3.12

[hugovk]

Currently in alpha 4, beta due in May, RC in July, final in October.

https://peps.python.org/pep-0693/

[codecov[bot]]

Codecov Report

Merging #123 (af91168) into main (2bc3f26) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #123   +/-   ##
=======================================
  Coverage   95.40%   95.40%           
=======================================
  Files           9        9           
  Lines         392      392           
=======================================
  Hits          374      374           
  Misses         18       18           

Flag	Coverage Δ
macos-latest	95.40% <ø> (ø)
ubuntu-latest	95.40% <ø> (ø)
windows-latest	95.40% <ø> (ø)

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[adriens]

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