changes for tox>=4.0 release

[zacharyburnett]

Closes #7383

This PR addresses the issue raised in #7383

Checklist for maintainers

• added entry in CHANGES.rst within the relevant release section
• updated or added relevant tests
• updated relevant documentation
• added relevant milestone
• added relevant label(s)
• ran regression tests, post a link to the Jenkins job below.
  How to run regression tests on a PR
• Make sure the JIRA ticket is resolved properly

[zacharyburnett]

since Tox 4.0 is using PEP517, we run into the C extension issue noted in #7386

[jdavies-st]

I think you can unpin tox everywhere and just do

[testenv:check-dependencies]
description = verify that install_requires in setup.cfg has correct dependencies
usedevelop = false
extras =
commands =
    verify_install_requires

For some reason the new version of tox doesn't install the jwst wheel when usedevelop=true. Also, we had (by mistake) been using test dependencies in this job, which was a mistake, so the test extras needs to be turned off. The whole point of the job is to make sure the dependencies are accounted for without the test extras installed.

It's important that the pyargs job has usedevelop=false. The others need usedevelop=true, as that's where they are picking up installed code (built C binaries) when we run pytest.

[zacharyburnett]

using package = wheel works as a PEP517-correct install with all of the C extensions; however, test-oldestdeps fails when the minimum_deps script tries to import jwst with pkg_resources

[zacharyburnett]

CI test success is blocked by #7386 and #7388

[zacharyburnett]

blocked by #7406

[zacharyburnett]

rebased and formatting changes, plus added an intermediate step to cache CRDS before testing

[codecov]

Codecov Report

Base: 78.65% // Head: 78.65% // No change to project coverage 👍

Coverage data is based on head (90aa708) compared to base (093ec3e).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7384   +/-   ##
=======================================
  Coverage   78.65%   78.65%           
=======================================
  Files         455      455           
  Lines       39168    39168           
=======================================
  Hits        30806    30806           
  Misses       8362     8362           

Flag	Coverage Δ		*Carryforward flag
nightly	78.64% <ø> (ø)		Carriedforward from 093ec3e
unit	51.33% <ø> (-0.07%)	⬇️

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