Fix ci mypy errros

[mauicv]

What is this

This PR fixes mypy errors that are arising in CI`

Note: Doc builds and licenses are failing. To be fixed in a different PR

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[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 85.16%. Comparing base (8a1eb1c) to head (681113b).
Report is 10 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1012      +/-   ##
==========================================
- Coverage   85.23%   85.16%   -0.08%     
==========================================
  Files          74       74              
  Lines        8834     8796      -38     
==========================================
- Hits         7530     7491      -39     
- Misses       1304     1305       +1     

Files	Coverage Δ
alibi/datasets/default.py	93.52% <100.00%> (+0.04%)	⬆️
alibi/explainers/pd_variance.py	98.37% <ø> (ø)
alibi/utils/visualization.py	47.79% <0.00%> (-0.31%)	⬇️

... and 7 files with indirect coverage changes