DEP: pinned sentencepiece to 0.1.91 in setup.py to fix build issues with newer versions
Author: jmwoloso
Pull request: yes

# What does this PR do?
Pins `sentencepiece` to `0.1.91` to resolve build issues with newer versions
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Fixes # (issue)
https://github.com/huggingface/transformers/issues/8020

## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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@LysandreJik 
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Comments:
I can check the other 3 boxes if needed. They didn't seem to apply to this particular PR so I left them unchecked.