Fix `return_attention_scores` bug (#1977) #6614

Job	Run time
Check the code format	2m 28s
Check the code format	2m 28s
Test the code (tensorflow, keras-stable)	22m 57s
Test the code (tensorflow, keras-stable)	22m 57s
Test the code (jax, keras-stable)	29m 10s
Test the code (jax, keras-stable)	29m 10s
Test the code (torch, keras-stable)	15m 54s
Test the code (torch, keras-stable)	15m 54s
Test the code (jax, keras-3.1)	28m 47s
Test the code (jax, keras-3.1)	28m 47s
Test the code (jax, keras-nightly)	24m 43s
Test the code (jax, keras-nightly)	30m 10s
	4h 13m 25s

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