Add minimum dependencies CI build

[jrbourbeau]

This PR adds a new CI build which runs the test suite against the minimum version of distributeds dependencies (similar to what we already do over in dask/dask). This will allow us to test, to the best of our ability, that our specified minimum versions are valid.

[jrbourbeau]

Note that:

• The minimum versions for click, psutil, and sortedcontainers were bumped to fix conda solve errors

• dask was bumped to avoid the issue reported here 2021.04.1 release community#150 (comment)

• toolz itself didn't need to be bumped, however there was a segmentation fault in CI due to cytoolz (which is pulled in from the dask conda package). Bumping the minimum toolz version indirectly leads to a correspondingly newer version of cytoolz being installed. Given that (cy)toolz=0.10.0 is almost two years old, I think this is okay

[jrbourbeau]

@crusaderky would you mind taking a look at this PR when you get a chance?

[crusaderky]

I think you should really have two separate tests:

1. test that everything works when pinning minimum version of various dependencies
2. test that everything works when you exclusively have the listed minimum dependencies (e.g. no numpy, pandas, bokeh)

ATM you're trying to do both in one test and as a result you're skipping a lot of tests - which significantly harms test coverage vs. minimum versions.

[jrbourbeau]

Circling back here, it'd be good to get a minimum dependency CI build into distributed. This would have helped us avoid the need for our recent 2022.10.2 hotfix release (xref dask/community#284). @charlesbluca this seems like the sort of thing you might enjoy -- do you have bandwidth / interest in getting this across the the finish line?

[charlesbluca]

Thanks for the ping @jrbourbeau! Yeah I can look into finishing this up