Add GitPython to quality tools
Adds gitpython to the `quality` command of the setup, as otherwise the quality tools cannot be used.

cc https://github.com/huggingface/transformers/pull/14379
Should we thus remove this line in the circleCI config?
```
            - run: pip install isort GitPython
```

It's there twice (code quality and repo consistency jobs).<|||||>Correct, just pushed the update. Thanks!