typo: fix typos in CONTRIBUTING.md and deepspeed.mdx
# What does this PR do?
Fix the following two typos
+ Missing line break after the third item in the Pull Request Checklist section of the CONTRIBUTING.md.
+ A typo error in the deepspeed.mdx file

## 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?
_The documentation is not available anymore as the PR was closed or merged._<|||||>The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_24184). All of your documentation changes will be reflected on that endpoint.