Update configuration_bart.py
Update following #19487 issue

![image](https://user-images.githubusercontent.com/49692939/195312422-1f70218d-ede7-48cc-9392-6bd7c02d1b87.png)


Tests passed
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_19517). All of your documentation changes will be reflected on that endpoint.