Adding the MacOS to CI

[john-science]

What is the change?

Adding the MacOS to CI.

Why is the change being made?

I recently found out that some of our users are Mac people.

Notes

1. I can not immediately get our unit tests working in Mac in parallel (something about our test temp directory logic breaks). So, this PR only runs the unit tests in series.
2. The Mac Unit Tests take 14 minutes to run. Is that too long?

---

Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify any new/changed code.

• The code style follows good practices.
• The commit message(s) follow good practices.

• The release notes have been updated if necessary.
• The documentation is still up-to-date in the doc folder.
• The dependencies are still up-to-date in pyproject.toml.

[opotowsky]

Looks good to me if you're happy with the run time!

[albeanth]

I've got an old macbook air from grad school lying around if you ever need more mac-specific testing.

If you're happy with the PR, push it through!

[john-science]

I've got an old macbook air from grad school lying around if you ever need more mac-specific testing.

I borrowed my wife's Mac. But I'm sure I'd love a second tester. Up to you! But it sounds like we've had Mac testers at USNC for years.