Add type hints for gptneox models
# What does this PR do?
Adding missing type hints for `GPTNeoxForCausalLM` and `GPTNeoXModel` as referenced in this issue.(https://github.com/huggingface/transformers/issues/16059#issuecomment-1164898772).

## Before submitting
- [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).
- [ ] Did you write any new necessary tests?

## Who can review?
Anyone in the community please feel free to review😄

@Rocketknight1

_The documentation is not available anymore as the PR was closed or merged._