FixAuxiliaryLossForDeformableDetr
# What does this PR do?
DeformableDetr does not work when auxiliary_loss=True.
Since Deformable Detr has list of class_embed, bbox_embed, this code will raise NotImplementedError.
```python
                intermediate = outputs.intermediate_hidden_states if return_dict else outputs[4]
                outputs_class = self.class_embed(intermediate)
                outputs_coord = self.bbox_embed(intermediate).sigmoid()
```
```python
outputs_class = self.class_embed(intermediate)
File "/opt/conda/lib/python3.8/site-packages/torch/nn/modules/module.py", line 1110, in _call_impl
return forward_call(*input, **kwargs)
File "/opt/conda/lib/python3.8/site-packages/torch/nn/modules/module.py", line 201, in _forward_unimplemented
raise NotImplementedError
NotImplementedError
```
To fix this, we can simply use predefined `outputs_class` and `outputs_coord` in this [line](https://github.com/huggingface/transformers/blob/main/src/transformers/models/deformable_detr/modeling_deformable_detr.py#L1943-L1944).

## 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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      Pull Request section?
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      to it if that's the case.
- [ ] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


## Who can review?

@NielsRogge 

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_The documentation is not available anymore as the PR was closed or merged._<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.<|||||>@NielsRogge Ping on this PR.<|||||>Hi @long8v would you be able to run `make fixup` from the root of the repo, and potentially rebase on the main branch to make the CI green?

Thanks!<|||||>I reuploaded this PR [here](https://github.com/huggingface/transformers/pull/20959)!