Add support for Python 3.12 (and adjust code for tokenizer changes).

[matthewwardrop]

closes: #196

[bashtage]

Is there any expectations the CI runs or needs to be passed?

[matthewwardrop]

Is there any expectations the CI runs or needs to be passed?

Yes... but it is struggling because Python 2.7 and 3.6 no longer exist in GitHub actions support versions. Fixing.

[codecov-commenter]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (6bd31ca) 98.49% compared to head (8853aee) 98.43%.

Files	Patch %	Lines
patsy/tokens.py	60.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #197      +/-   ##
==========================================
- Coverage   98.49%   98.43%   -0.07%     
==========================================
  Files          30       30              
  Lines        3131     3132       +1     
  Branches      690      691       +1     
==========================================
- Hits         3084     3083       -1     
- Misses         24       25       +1     
- Partials       23       24       +1     

Flag	Coverage Δ
unittests	98.02% <60.00%> (-0.07%)	⬇️

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