[Doctest] Add configuration_fsmt.py
Author: sha016
Pull request: yes

# What does this PR do?
Adds `configuration_fsmt.py` to `utils/documentation_tests.txt`
Based on https://github.com/huggingface/transformers/issues/19487

@ydshieh please review, thanks!

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Fixes # (issue)


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Comments:
_The documentation is not available anymore as the PR was closed or merged._

This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.

@sha016 I force pushed to this PR with a tiny update.
Once @sgugger approves this PR, we can merge it to `main`.

Thank you again for the contribution!