Remove set_access_token usage + fail tests if FutureWarning
`set_access_token` is deprecated and will be removed in `huggingface_hub>=0.14`.

This PR removes it from the tests (it was not used in `transformers` source code itself). In the future, use `set_git_credential` if needed. It is a git-credential-agnostic helper, i.e. you can store your git token in `git-credential-cache`, `git-credential-store`, `osxkeychain`, etc. The legacy `set_access_token` was only able to set in `git-credential-store` no matter the user preference.

(for context, I found out about this while working on https://github.com/huggingface/huggingface_hub/pull/1381)

---

In addition to this, I have added

```
filterwarnings =
    error::FutureWarning:huggingface_hub*
```

to the `setup.cfg` config file to fail on future warnings from `huggingface_hub`. In `hfh`'s CI we trigger on FutureWarning from any package but it's less robust (any package update leads can lead to a failure). No obligation to keep it like that (I can remove it if you prefer) but I think it's a good idea in order to track future FutureWarnings.
_The documentation is not available anymore as the PR was closed or merged._