Fixing tests for perceiver (texts)
Author: Narsil
Pull request: yes

# What does this PR do?

Fixes the tests by supporting `input_ids` on PerceiverForSequenceClassification&co.

If both `inputs` and `input_ids` are supplied, crash with an error.

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Fixes # (issue)


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [ ] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md#start-contributing-pull-requests),
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- [ ] Did you write any new necessary tests?


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