Fix: Return Attention Scores when return_attention_scores=True

[Furkan-rgb]

This pull request addresses an issue in the Attention layer where the return_attention_scores parameter wasn't correctly handled in the compute_output_shape method. This fix ensures that attention scores are returned when return_attention_scores=True.

Changes Made

Modified compute_output_shape method to return the shape of both the attention output and the attention scores when return_attention_scores=True.

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 66.66667% with 9 lines in your changes missing coverage. Please review.

Project coverage is 81.96%. Comparing base (3dd958b) to head (8a66542).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
keras/src/layers/attention/attention.py	66.66%	6 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #20684      +/-   ##
==========================================
- Coverage   81.97%   81.96%   -0.01%     
==========================================
  Files         544      544              
  Lines       50751    50773      +22     
  Branches     7851     7854       +3     
==========================================
+ Hits        41604    41617      +13     
- Misses       7252     7258       +6     
- Partials     1895     1898       +3     

Flag	Coverage Δ
keras	81.80% <66.66%> (-0.01%)	⬇️
keras-jax	63.94% <66.66%> (-0.01%)	⬇️
keras-numpy	58.87% <66.66%> (+<0.01%)	⬆️
keras-openvino	29.93% <7.40%> (-0.01%)	⬇️
keras-tensorflow	64.69% <66.66%> (-0.01%)	⬇️
keras-torch	63.79% <66.66%> (-0.01%)	⬇️

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[fchollet]

Thanks for the PR! Can you add a unit test, so we avoid breaking this in the future?

[fchollet]

LGTM, thank you!