Fix Tensorflow T5 with int64 input
Our Tensorflow T5 model uses constant values that are initialized with `tf.constant()` or just from Python int literals. Tensorflow guesses the dtype in both of these cases as `int32`, which causes the operations using them to fail if `int64` input is supplied.

This PR adds checks that cast the constants to the dtype of the inputs, to ensure that the operations succeed for both `int32` and `int64` inputs.