[santisoler]

Summary

Fix sphinx-gallery config by passing the "FileNameSortKey" string instead of the actual class. This makes its configuration pickable, and therefore cacheable.

PR Checklist

• If this is a work in progress PR, set as a Draft PR
• Linted my code according to the style guides.
• Added tests to verify changes to the code.
• Added necessary documentation to any new functions/classes following the
  expect style.
• Marked as ready for review (if this is was a draft PR), and converted
  to a Pull Request
• Tagged @simpeg/simpeg-developers when ready for review.

Reference issue

What does this implement/fix?

Additional information

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.75%. Comparing base (e203ecf) to head (d623729).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1786      +/-   ##
==========================================
- Coverage   81.75%   81.75%   -0.01%     
==========================================
  Files         425      425              
  Lines       55773    55773              
  Branches     5298     5298              
==========================================
- Hits        45600    45598       -2     
- Misses       8761     8762       +1     
- Partials     1412     1413       +1     

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