Fix for issue #21118: inconsistent behavior across callbacks

[adar21a]

#21118

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 82.85714% with 6 lines in your changes missing coverage. Please review.

Project coverage is 82.57%. Comparing base (cbb3682) to head (e32ecf3).

Files with missing lines	Patch %	Lines
keras/src/callbacks/model_checkpoint.py	82.85%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #21275   +/-   ##
=======================================
  Coverage   82.57%   82.57%           
=======================================
  Files         564      564           
  Lines       54629    54649   +20     
  Branches     8495     8504    +9     
=======================================
+ Hits        45108    45125   +17     
- Misses       7432     7434    +2     
- Partials     2089     2090    +1     

Flag	Coverage Δ
keras	82.38% <82.85%> (+<0.01%)	⬆️
keras-jax	63.64% <82.85%> (+<0.01%)	⬆️
keras-numpy	58.74% <8.57%> (-0.02%)	⬇️
keras-openvino	33.00% <8.57%> (-0.01%)	⬇️
keras-tensorflow	64.05% <82.85%> (+<0.01%)	⬆️
keras-torch	63.71% <82.85%> (+<0.01%)	⬆️

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[fchollet]

Thanks for the PR!

[fchollet]

Can we refactor this logic into a standalone function that we could reuse across all callbacks that need this functionality?