ci: use local mypy

[kmichel-aiven]

This removes duplicate dependency definitions and detects more errors.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.88%. Comparing base (3aa93a8) to head (cd02dff).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #201      +/-   ##
==========================================
- Coverage   78.90%   78.88%   -0.03%     
==========================================
  Files         142      142              
  Lines       10173    10168       -5     
==========================================
- Hits         8027     8021       -6     
- Misses       2146     2147       +1     

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