Remove actions/cache in favor of actions/setup-python caching

[kurtmckee]

Description:

Currently, all CI jobs emit warnings due to actions/cache@v3, which uses an old Node.js version (recent example).

However, on inspection, it appears that actions/cache is configured incorrectly:

• There are no lock files for it to hash, resulting in a blank portion in the cache key (caches generated in CI).

  

• The comments in the YAML claim that it's caching for pipenv, but then caches the pip directory instead.

  

Therefore, this PR rips out actions/cache in favor of the Python caching already supported by actions/setup-python.

If this merges, please close #284.

PR Checklist:

• Code is formatted and linted (run pre-commit run --all-files)
• Tests pass (run make test)
  n/a
• Documentation has been updated to reflect changes, if applicable
  n/a
• Changes are added to the changelog
  n/a

[jonhealy1]

Thanks