Improve future compatibility of `CLIPMultiHeadAttention` #6586

Job	Run time
Check the code format	2m 26s
Test the code (tensorflow, keras-stable)	23m 32s
Test the code (jax, keras-stable)	27m 7s
Test the code (torch, keras-stable)	16m 14s
Test the code (jax, keras-3.1)	26m 43s
Test the code (jax, keras-nightly)	27m 59s
	2h 4m 1s

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