Fix TF CTC tests
# What does this PR do?

(see title)
_The documentation is not available anymore as the PR was closed or merged._<|||||>@ydshieh before @amyeroberts work in #21502 these tests had no overwrite, correct. However, see the note in Amy's PR -- the labels were not correctly handled, which meant that `test_dataset_conversion` was probably terminating early [here](https://github.com/huggingface/transformers/blob/edc1e734bfc01109b8c66881d950ebbda032a6d2/tests/test_modeling_tf_common.py#L1815), which would explain the ausence of crashes prior to the PR :)<|||||>Thanks for the fix @gante ! 

@ydshieh Yes, Joao's correct. There's three different cases where the state of the tests changed: 
* For `test_loss_computation`, the previous test was being skipped. [The given reason](https://github.com/huggingface/transformers/blob/6f79d264422245d88c7a34032c1a8254a0c65752/tests/models/hubert/test_modeling_tf_hubert.py#L327) was incorrect shapes - however, at the time of adding #21502 the returned loss was actually `None`.
* Some tests were being skipped by overloading [with an empty test](https://github.com/huggingface/transformers/blob/6f79d264422245d88c7a34032c1a8254a0c65752/tests/models/hubert/test_modeling_tf_hubert.py#L313) rather than `unittest.skip` and so previously showed as passing.
* The branch calculating loss wasn't being touched when fitting the model - `input_values` passed in as a dictionary - as `labels` was [taken from keyword arguments, rather than `outputs['labels']`](https://github.com/huggingface/transformers/blob/6f79d264422245d88c7a34032c1a8254a0c65752/src/transformers/models/hubert/modeling_tf_hubert.py#L1640). This meant some tests e.g. [`test_keras_fit` in TFModelTesterMixin](https://github.com/huggingface/transformers/blob/6f79d264422245d88c7a34032c1a8254a0c65752/tests/test_modeling_tf_common.py#L1526) previously passed as the memory intensive operation was skipped.  