[Generate] Correct input_ids detection
Author: patrickvonplaten
Pull request: yes

# What does this PR do?

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A test whether the input is `input_ids` is incorrect. Good that our RAG tests are pretty aggressive to spot such small differences

## 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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Models:

- albert, bert, xlm: @LysandreJik
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Comments:
Thanks for fixing!