Run tests with minimum versions of dependencies installed

[ichard26]

Follow-up from #2791 and #2774, we should add a step to the test workflow which runs the test suite again but with the lowest supported dependencies installed. Unfortunately there doesn't really seem to be good tooling for this (short of https://github.com/ffy00/python-resolver#mindeps-cli) so this may be blocked until such tooling exists or we could take the cheap to implement / more expensive down the road route of defining a constraints file that manually pins the dependencies to the lowest versions supported.

We could run diff-shades/primer against the minimum dependencies but I'm wary of the CI time increases. Especially as it's unlikely an older version of a dependency would cause a subtle issue with formatting (given the core formatting logic is all our own) that these sorts of jobs discover.

[JelleZijlstra]

Thanks! I agree primer is overkill; our dependencies are unlikely to affect formatting since the core formatting logic doesn't use any dependencies.

[hauntsaninja]

There's https://pypi.org/project/pessimist/ but I don't have direct experience with using it.