Switch back to upstream mypy

[cdce8p]

Followup to #10527

Mypy just released 1.18.1 which includes the required match statement fixes.
https://mypy-lang.blogspot.com/2025/09/mypy-1181-released.html

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.90%. Comparing base (169ffd6) to head (957764b).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #10549   +/-   ##
=======================================
  Coverage   95.90%   95.90%           
=======================================
  Files         177      177           
  Lines       19368    19368           
=======================================
  Hits        18574    18574           
  Misses        794      794           

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