TST: Fix tox for pyargs (try 2)

[pllim]

Exorcise zero coverage (try 2). Follow-up of #9550

• close Test codecov coverage pre-9550 #9651
• close Revert "TST: Remove pyargs from toxenv" #9649
• close TST: Fix tox for pyargs #9652

Tasks

• If you have a specific reviewer in mind, tag them.
• add a build milestone, i.e. Build 12.0 (use the latest build if not sure)
• Does this PR change user-facing code / API? (if not, label with no-changelog-entry-needed)
  • write news fragment(s) in changes/: echo "changed something" > changes/<PR#>.<changetype>.rst (see changelog readme for instructions)
  • update or add relevant tests
  • update relevant docstrings and / or docs/ page
  • start a regression test and include a link to the running job (click here for instructions)
    • Do truth files need to be updated ("okified")?
      • after the reviewer has approved these changes, run okify_regtests to update the truth files
• if a JIRA ticket exists, make sure it is resolved properly

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.11%. Comparing base (8409d2b) to head (0c73894).
⚠️ Report is 362 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##            main    #9660       +/-   ##
==========================================
+ Coverage   0.00%   79.11%   +79.11%     
==========================================
  Files        367      368        +1     
  Lines      37332    37222      -110     
==========================================
+ Hits           0    29447    +29447     
+ Misses     37332     7775    -29557     

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[pllim]

I think this is the correct fix. Turns out jwst wasn't running the test suite in true isolated env from clean directory outside of source tree. Now all jobs use the consistent pyargs setup and the coverage number is back.

But again, please review logs carefully in case I missed something. Thanks for your patience!

[pllim]

p.s. Turns out regression test suite isn't using tox at all, so no need to run RT. (Which brings me to my next PR that I am about to open... #9661)

[braingram]

Thanks! Quick merge before the test number changes again 😛