run_audio_classification.py freeze_base_model in w2v-bert

[HERIUN]

What does this PR do?

In audio classification using wav2vec. it needs freeze_base_model in w2v-bert

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• Did you write any new necessary tests?

Who can review?

@ylacombe

[LysandreJik]

cc @eustlb