[Python] Pin keras version for tensorflow inference test

[riteshghorse]

Fixes #30613

Pin keras version for tf_inference_it_test in postcommits to less than 3.0.0. Created #30616 to support Keras 3.

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[riteshghorse]

Tests are now passing

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[tvalentyn]

We should unpin the version after #30616 is fixed , precisely to detect issues like this. Can you add a TODO?

[tvalentyn]

LGTM otherwise

[riteshghorse]

Yes, added that as part of the task itself. Thanks!