Use separate conda cache directories in CI

[altheaden]

This PR updates the build workflow to use separate directories for each python version for conda caching. Issues with this seem to have been crashing CI runs lately.

I also fixed a bug in the docs workflow, where it was referring to a nonexistent python version matrix (likely a remnant of copying from the build workflow). Instead, I set this to be an environment variable called PYTHON_VERSION which will allow us to more easily specify and update the python version we use for the documentation without having to change it in a couple different places. I also copied this convention into the pre-commit update workflow for consistency.

Checklist

• Documentation has been built locally and changes look as expected
• Testing comment in the PR documents testing used to verify the changes

[altheaden]

Testing

I ran all CI workflows on my fork and verified that I did see the correct python versions, and also that the cache directories were set up correctly. I also checked that the documentation appears to have been built and deployed correctly. All checks passed.

[altheaden]

@xylar I made one additional change in the CI here that I'd like to repeat across other repos as well. Can you verify that the changes I made here are in line with what you'd like? If so, I will go ahead and implement this on other repos.
Most of the repos I've been working on have fail-fast already set so that's why it's not present here and might not be present in many others either.

[xylar]

Looks great! Thank you!

[xylar]

@xylar I made one additional change in the CI here that I'd like to repeat across other repos as well. Can you verify that the changes I made here are in line with what you'd like? If so, I will go ahead and implement this on other repos.

Yes, perfect. The more we can bundle into one PR, the better to save us time.

Most of the repos I've been working on have fail-fast already set so that's why it's not present here and might not be present in many others either.

Okay, good to know. I noticed it on Compass and it was pretty annoying so I wanted to catch it wherever it's still on.