Remove call to deprecated fit_loop

[christopherfish]

What does this PR do?

train_loop was renamed to fit_loop, but an internal call to train_loop remained causing warnings. This PR fixes those calls.

This PR is a similar fix (to the same file!) #8434

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

None

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[codecov]

Codecov Report

Merging #8873 (a158bf5) into master (5fd157e) will decrease coverage by 4%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #8873    +/-   ##
=======================================
- Coverage      93%     89%    -4%     
=======================================
  Files         169     169            
  Lines       14078   14078            
=======================================
- Hits        13052   12474   -578     
- Misses       1026    1604   +578     

[awaelchli]

Thanks @christopherfish !!