 Addition of test code for GPTNeoX Flax support
@sanchit-gandhi

I have added a test code for the GPTNeoX Flax support #22950. 

I implemented it based on a fork at https://github.com/OhadRubin/transformers the above PR and [Flax GPT-Neo](https://github.com/gojiteji/transformers/blob/fix_flax_gpt_neox/tests/models/gpt_neo/test_modeling_flax_gpt_neo.py) test code.

During the execution of the tests based on [the doc](
https://huggingface.co/docs/transformers/add_new_model#2-next-prepare-your-environment), the log displayed the following output:

```
platform linux -- Python 3.9.16, pytest-7.3.1, pluggy-1.0.0
rootdir: /myhomedir/transformers
configfile: setup.cfg
plugins: anyio-3.6.2
collected 43 items

tests/models/gpt_neox/test_modeling_flax_gpt_neox.py sssssssssssssssssssssssssssssssssssssssssss [100%]

=================================================== 43 skipped in 1.97s ===================================================
```
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_24002). All of your documentation changes will be reflected on that endpoint.<|||||>Hey @gojiteji! Thanks for picking-up the Flax GPT Neo PR! Would you mind rebasing onto main:
```
git fetch upstream
git rebase upstream main
```

And then force pushing the changes:
```
git push -f origin fix_flax_gpt_neox
```

This will then isolate the changes from your PR amongst the other ones<|||||>Hey @gojiteji - not sure if you pushed or force pushed? See previous comment: https://github.com/huggingface/transformers/pull/24002#issuecomment-1577141369

Let's see if we can revive the commit history here. In the case that we can't, we probably need to open a new PR for this<|||||>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.<|||||>Hey @gojiteji - feel free to open a new PR for this if you still want to continue the integration. Currently not sure which bits are new since the commit history is broken, but am more than happy to help with any questions / queries on a fresh PR!<|||||>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.