Enable SparseCategoricalCrossentropy to accept and propagate axis

[edge7]

No description provided.

[edge7]

This is mainly to accommodate issue #21097
By the way, it does not completely fix it, as I have not modified the squeeze part, which means the target still needs to be something like (BATCH_SIZE, N, W) and not (BATCH_SIZE, 1, N, W)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 82.69%. Comparing base (e1c59ff) to head (bec7485).

Files with missing lines	Patch %	Lines
keras/src/backend/torch/nn.py	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #21104   +/-   ##
=======================================
  Coverage   82.68%   82.69%           
=======================================
  Files         564      564           
  Lines       54128    54130    +2     
  Branches     8411     8411           
=======================================
+ Hits        44758    44764    +6     
+ Misses       7295     7293    -2     
+ Partials     2075     2073    -2     

Flag	Coverage Δ
keras	82.50% <66.66%> (+<0.01%)	⬆️
keras-jax	64.03% <0.00%> (+<0.01%)	⬆️
keras-numpy	59.10% <0.00%> (+<0.01%)	⬆️
keras-openvino	32.88% <0.00%> (-0.01%)	⬇️
keras-tensorflow	64.35% <0.00%> (+<0.01%)	⬆️
keras-torch	64.08% <66.66%> (+<0.01%)	⬆️

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[fchollet]

LGTM, thanks