refactor for Tox 4

[zacharyburnett]

update tox.ini and also update version of used GitHub Actions

[codecov]

Codecov Report

Base: 86.83% // Head: 86.84% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (9bdf3fc) compared to base (f4ff623).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #428   +/-   ##
=======================================
  Coverage   86.83%   86.84%           
=======================================
  Files          23       24    +1     
  Lines        3759     3769   +10     
=======================================
+ Hits         3264     3273    +9     
- Misses        495      496    +1     

Flag	Coverage Δ
unit	86.84% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
setup.py	0.00% <0.00%> (ø)
gwcs/spectroscopy.py	97.79% <0.00%> (+0.13%)	⬆️
gwcs/selector.py	92.94% <0.00%> (+0.32%)	⬆️

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[mcara]

I have no idea what I am approving but if tests pass, that's fine with me

[WilliamJamieson]

The names of CI jobs have changed, which means the required jobs will need to be updated.

LGTM