chore: drop Python 3.11 support

[feanil]

Summary

• Drops Python 3.11 from CI test matrix, pypi-release workflow, and tox envlist
• Updates coverage step condition from 3.11 to 3.12
• Removes 3.11 trove classifier from setup.py
• Regenerates pinned requirements using Python 3.12
• Bumps version to 2.5.1

Part of openedx/public-engineering#499

Test plan

• CI passes with Python 3.12

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 55.35%. Comparing base (4500f8a) to head (31c5c8e).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #347   +/-   ##
=======================================
  Coverage   55.35%   55.35%           
=======================================
  Files           3        3           
  Lines          56       56           
=======================================
  Hits           31       31           
  Misses         25       25           

Flag	Coverage Δ
unittests	55.35% <100.00%> (ø)

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