Fix for issue #21118: inconsistent behavior across callbacks

[adar21a]

#21118

[google-cla]

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 80.00000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 82.69%. Comparing base (6d26efb) to head (acec574).

Files with missing lines	Patch %	Lines
keras/src/callbacks/model_checkpoint.py	80.00%	3 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #21124      +/-   ##
==========================================
- Coverage   82.69%   82.69%   -0.01%     
==========================================
  Files         564      564              
  Lines       54132    54152      +20     
  Branches     8411     8420       +9     
==========================================
+ Hits        44765    44779      +14     
- Misses       7294     7297       +3     
- Partials     2073     2076       +3     

Flag	Coverage Δ
keras	82.50% <80.00%> (-0.01%)	⬇️
keras-jax	64.08% <80.00%> (+<0.01%)	⬆️
keras-numpy	59.08% <8.57%> (-0.02%)	⬇️
keras-openvino	32.87% <8.57%> (-0.01%)	⬇️
keras-tensorflow	64.36% <80.00%> (+<0.01%)	⬆️
keras-torch	64.12% <80.00%> (+<0.01%)	⬆️

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[gbaned]

Hi @adar21a Can you please sign CLA? Thank you!

[fchollet]

Thanks for the PR! Please add a unit test for the fixed use cases.