Fix scheduled TF Speech tests
CI logs: https://github.com/huggingface/transformers/runs/3501334018?check_suite_focus=true

**Context**
Doing `import soundfile as sf` was causing `OSError: sndfile library not found` on all integration tests for `TFWav2Vec2` and `TFHubert`

**Solution**
This PR adds `libsndfile` as a dependency for the TF jobs, like it was done for the Pytorch counterparts.

CC @patrickvonplaten 
Thanks a lot for taking care of it