Update testing suite

[Zeitsperre]

Pull Request Checklist:

• [ ] This PR addresses an already opened issue (for bug fixes / features)

  • This PR fixes issue #xyz

• [x] Tests for the changes have been added (for bug fixes / features)

• [x] Documentation has been added / updated (for bug fixes / features)

• [x] HISTORY.rst has been updated (with summary of main changes)

• [x] I have added my relevant user information to AUTHORS.md

• What kind of change does this PR introduce?:

• Removes some long-obsolete tests

• Splits the conda CI job to test against xarray-stable and xarray-dev

• Updates condaf CI jobs to use provision-with-micromamba with caching

• Sets versions for pytest-loguru, sphinx_rtd_theme, and black that are more current

• pytest is now always in colour

• toxv@v3.0 is now set until tox-conda supports tox@v4.0

• Does this PR introduce a breaking change?:

Not really, no.

• Other information:

[cehbrecht]

@Zeitsperre sounds good to use micromamba :) Does the test 3.9 fail due to incompatibilities with the latest xarray? Should the upstream test be allowed to fail?

[Zeitsperre]

@cehbrecht

That's precisely the reason why the conda-build is failing (I'm going to rename the tests to add the upstream flag for clarity here). I don't think the upstream build should be a blocker to merging a PR (it's something the maintainers need to keep an eye, not the contributors).

As it stands, the only thing blocking merge is an approving review. If we want to make some builds "required" in order to merge (like we have on xclim) that's something we could do. Thoughts?

[cehbrecht]

@Zeitsperre I thought we could have an xfail for the upstream test ...

[Zeitsperre]

@cehbrecht

Thanks for the approval. Merging now.

We can set things up that way (technically, it's already setup that way). If we set the build to continue-on-failure, We won't see the red X-mark any more (which defeats the purpose in my mind; we don't know if it failed unless we look for ourselves). Neither solution seems ideal.