Workflow for testing on macOS

[jwodder]

Closes #4942.

[codecov]

Codecov Report

Merging #4947 into maint will decrease coverage by 0.01%.
The diff coverage is 41.66%.

@@            Coverage Diff             @@
##            maint    #4947      +/-   ##
==========================================
- Coverage   89.68%   89.67%   -0.02%     
==========================================
  Files         289      289              
  Lines       40488    40500      +12     
==========================================
+ Hits        36312    36317       +5     
- Misses       4176     4183       +7     

Impacted Files	Coverage Δ
datalad/tests/utils.py	86.51% <30.00%> (-0.64%)	⬇️
datalad/core/distributed/tests/test_push.py	97.98% <100.00%> (+0.01%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 021aa5f...83adb0f. Read the comment docs.

[yarikoptic]

Great. Please add known_failure_githubci_osx similar to known_failure_githubci_win and decorate those two failing tests with it so we get green at least and proceed. IMHO ideally this one should be positioned against maint branch (not master) since would be of benefit there.

[jwodder]

@yarikoptic Done.

[yarikoptic]

I think more green runs is good, so I will proceed with merge.
Could you please try to add codecov submission in a follow up PR? There was something not working for windows workflow https://github.com/datalad/datalad/blob/master/.github/workflows/test_win2019_disabled#L59 but may be it would work for osx?