Ability to resume workflow when codecov push fails

[AlexVCaron]

Quick description

Codecov is not super stable right now. When the coverage upload fails, we need to re-run the whole test suite (long). This PR splits the workflow in twain, so only the second job fails when codecov push fails. Then, to retry the upload, re-run the workflow, specifying to run ONLY the failed jobs. Voilà ?

Type of change

Check the relevant options.

• New feature (non-breaking change which adds functionality)

Checklist

• My code follows the style guidelines of this project (run autopep8)
• I added relevant citations to scripts, modules and functions docstrings and descriptions
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I moved all functions from the script file (except the argparser and main) to scilpy modules
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1c4b850) 65.92% compared to head (747da90) 68.12%.
Report is 13 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #909      +/-   ##
==========================================
+ Coverage   65.92%   68.12%   +2.20%     
==========================================
  Files         386      386              
  Lines       21573    20678     -895     
  Branches     3540     3160     -380     
==========================================
- Hits        14222    14087     -135     
+ Misses       5720     5326     -394     
+ Partials     1631     1265     -366     

Components	Coverage Δ
Scripts	70.68% <ø> (+3.40%)	⬆️
Library	63.76% <ø> (+0.29%)	⬆️