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

# What does this PR do?

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Fixes # (issue)


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Please refer to issue #30571 


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Comments:
cc @ArthurZucker @younesbelkada 

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_30573). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

Hi @younesbelkada, @amyeroberts, could you please review if this PR is ready for merging? If everything is in order, could you merge it? Thank you for your time!