fix:missing `output_router_logits` in SwitchTransformers
Author: lausannel
Pull request: yes

# What does this PR do?

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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).
- [x] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#create-a-pull-request),
      Pull Request section?
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- [ ] Did you write any new necessary tests?

Please see the problem with #30571 


## Who can review?

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@ArthurZucker 

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