remove flag to use pip 2020 solver from Github Action pip install command on OSX

[valeriupredoi]

Description

That flag will introduce an error in pip=21.0 so let's just get rid of it (it is now the default solver, so all's safe and sound). See example warning

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[codecov]

Codecov Report

Merging #1357 (f401e81) into main (4b8bf66) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1357   +/-   ##
=======================================
  Coverage   89.59%   89.59%           
=======================================
  Files         196      196           
  Lines       10273    10273           
=======================================
  Hits         9204     9204           
  Misses       1069     1069           

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[bvreede]

I turned on tests for this PR, but tests now fail -- regardless of the presence of the feature resolver flag. Not sure what is up, but failing tests is a bad sign I'd say :)

[valeriupredoi]

cheers @bvreede - they are indeed failing and the fails are not related to this PR (neither the solver) but to #1358 and the linked issue with the new pip - not a worry, the solver opt is good to be removed, it's pip they need to sort out their stuff 😁 You can try force pip 21.2.4 and see all goes fine 👍

[zklaus]

@bvreede that was indeed due to the broken pip and is fixed now. Could you have another look?

[valeriupredoi]

@schlunma you mind giving me a quick review here please mate? We need to get this in ideally for the release 🍺

[schlunma]

Can you briefly explain what --use-feature=2020-resolver was supposed to achieve and why we can remove it now?

Apart from that the changes look fine to me!

[valeriupredoi]

@schlunma yis, good point! Pip introduced a more robust but different dependency resolver back when were were all working from home (sneaky! 😁 ), see communication release and that was breaking some stuffs back then, now it's the default resolver and the call to use the older resolver is deprecated and will introduce an error if used 👍 🍺

[schlunma]

Cheers, thanks for the explanation!

[valeriupredoi]

cheers much for reviewing, Manu! 🍺