Added Doctest for Deberta Pytorch
Author: Tegzes
Pull request: yes

# What does this PR do?
Adds Doctest for DeBerta [Pytorch version]

Issue: #16292


## Before submitting
- [x] 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#start-contributing-pull-requests),
      Pull Request section?
- [x] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case.
- [x] 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).
- [x] Did you write any new necessary tests?


## Who can review?
@ydshieh @patrickvonplaten


Comments:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_17997). All of your documentation changes will be reflected on that endpoint.

The doctest pass locally. I will look the changes in this PR :-) 

Hi @Tegzes, Thank you for this PR!

- For `DebertaForMaskedLM`, is there any reason to use `lsanochkin/deberta-large-feedback` instead of `_CHECKPOINT_FOR_DOC = "microsoft/deberta-base"`?

- In order to fix the tests (see the end), could you try to use variable names like
  ```
  _CHECKPOINT_FOR_SEQUENCE_CLASSIFICATION
  _CHECKPOINT_FOR_TOKEN_CLASSIFICATION
  _CHECKPOINT_FOR_QA
  ```
  See, for example, the doctest for `mobilebert` https://github.com/huggingface/transformers/blob/f681437203baa7671de3174b0fa583c349d9d5e1/src/transformers/models/mobilebert/modeling_mobilebert.py#L59-L78
  - You will need something new like `_MASKED_LM_EXPECTED_OUTPUT`, `_MASKED_LM_EXPECTED_LOSS` etc.
  - You will also have to work on the corresponding places in `DebertaV2` - as it has some code copied from `Deberta`

Let us know if you need more information.






### The errors in `ci/circleci: check_repository_consistency`		
```
- src/transformers/models/deberta_v2/modeling_deberta_v2.py: copy does not match models.deberta.modeling_deberta.DebertaForMaskedLM at line 1094
- src/transformers/models/deberta_v2/modeling_deberta_v2.py: copy does not match models.deberta.modeling_deberta.DebertaForSequenceClassification at line 1230
- src/transformers/models/deberta_v2/modeling_deberta_v2.py: copy does not match models.deberta.modeling_deberta.DebertaForTokenClassification at line 1350
- src/transformers/models/deberta_v2/modeling_deberta_v2.py: copy does not match models.deberta.modeling_deberta.DebertaForQuestionAnswering at line 1427

```

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.


> * For `DebertaForMaskedLM`, is there any reason to use `lsanochkin/deberta-large-feedback` instead of `_CHECKPOINT_FOR_DOC = "microsoft/deberta-base"`?

Hi @ydshieh, I used this model because it was the only one returning the correct output (from what I've tested)



> * In order to fix the tests (see the end), could you try to use variable names like
>   ```
>   _CHECKPOINT_FOR_SEQUENCE_CLASSIFICATION
>   _CHECKPOINT_FOR_TOKEN_CLASSIFICATION
>   _CHECKPOINT_FOR_QA
>   ```

All right! Thanks! I will make the changes and open another pull request