Test against PyPy 3.11

[jwodder]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.31%. Comparing base (9d13a79) to head (707900a).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #20   +/-   ##
=======================================
  Coverage   99.31%   99.31%           
=======================================
  Files           6        6           
  Lines         585      585           
  Branches      132      132           
=======================================
  Hits          581      581           
  Misses          3        3           
  Partials        1        1           

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