Allow for exit 68 for ping on mac

[yarikoptic]

per

• Unify two largely duplicate test workflows into one and add macos into matrix of OSes #31 (comment)

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.

Project coverage is 75.89%. Comparing base (0e00255) to head (35d69f2).
Report is 10 commits behind head on master.

Files with missing lines	Patch %	Lines
tests/test_command_runner.py	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #32      +/-   ##
==========================================
- Coverage   76.17%   75.89%   -0.28%     
==========================================
  Files           2        2              
  Lines        1024     1029       +5     
==========================================
+ Hits          780      781       +1     
- Misses        244      248       +4     

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[deajan]

Happy to know that from now on, tests will run on mac ^^
Thank you for the time and effort.