Callback on_train_batch_begin/end not called during fit()

[zazula]

on_train_batch_begin() and on_train_batch_end() are not being called on callbacks.

on_batch_begin() and on_batch_end() are being called and are the workaround.

That is, this does not work:
tf.keras.callbacks.LambdaCallback(on_train_batch_end=lambda batch, logs: do_something())

but this does:
tf.keras.callbacks.LambdaCallback(on_batch_end=lambda batch, logs: do_something())

tensorflow: 2.4.0-rc0