Prepare version 3.1.1

[dfremont]

The CI is currently failing because it's pulling in pygame from VerifAI, but I need to make a new release of Scenic before I can make a new release of VerifAI with the switch to pygame-ce. I've tested with tox locally so everything should be OK; if the CI problem doesn't resolve after making both releases, we can yank as needed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.71%. Comparing base (be35aea) to head (8762ee8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #465      +/-   ##
==========================================
- Coverage   89.76%   89.71%   -0.05%     
==========================================
  Files          48       48              
  Lines       13226    13226              
==========================================
- Hits        11872    11866       -6     
- Misses       1354     1360       +6     

see 2 files with indirect coverage changes

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