fix flaubert tokenizer
# What does this PR do?

Fix an issue from #19330, see the comments in the changes.

Current test failure [here](https://github.com/huggingface/transformers/actions/runs/3231701081/jobs/5291558259)
```bash
E               if self.do_lowercase:
E           AttributeError: 'FlaubertTokenizer' object has no attribute 'do_lowercase'
```


_The documentation is not available anymore as the PR was closed or merged._