Fix mypy typing for utilities.apply_func

[stancld]

What does this PR do?

Part of #7037. This PR disentangles large #7218. It fixes mypy typing in utilities.apply_func.py

Does your PR introduce any breaking changes? If yes, please list them.

None

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[codecov]

Codecov Report

Merging #8781 (a834848) into master (0752bcd) will decrease coverage by 4%.
The diff coverage is 94%.

@@           Coverage Diff           @@
##           master   #8781    +/-   ##
=======================================
- Coverage      92%     88%    -4%     
=======================================
  Files         176     176            
  Lines       14744   14788    +44     
=======================================
- Hits        13556   13024   -532     
- Misses       1188    1764   +576     

[tchaton]

LGTM !