Include xarray pinning in setup.cfg

[anissa111]

PR Summary

Closes #453

PR Checklist

General

• Make an issue if one doesn't already exist
• Link the issue this PR resolves by adding closes #XXX to the PR description where XXX is the number of the issue.
• Add a brief summary of changes to docs/release-notes.rst
• Add appropriate labels to this PR
• Make your changes in a forked repository rather than directly in this repo
• Passes precommit. To set up on your local, run pre-commit install from the top level of the repository. To manually run pre-commits, use pre-commit run --all-files and re-add any changed files before committing again and pushing.

[kafitzgerald]

Thanks for getting this in! I should've just done this yesterday when it came up, but oh well - thank you.

And looks good. If this fails, we've got bigger problems.

[anissa111]

Thanks for getting this in! I should've just done this yesterday when it came up, but oh well - thank you.

And looks good. If this fails, we've got bigger problems.

Haha, it will fail if a make a link typo 😅