add macos to CI

[kojix2]

Hi.

I added a workflow for macOS to Actions on GitHub based on (#494) by @sampsyo.
This workflow successfully builds odgi, but still fails testing.

[subwaystation]

What is the problem here @kojix2 ? I can't see any logs.

[subwaystation]

I also can't restart the CI, to reproduce the error. Weird.

[subwaystation]

Could you push another commit @kojix2? I don't have the rights on your branch. Maybe also give the macos build 2 threads.

[kojix2]

Rebased commit on master branch.
I will close this pull request, but you can see the build log above.

[subwaystation]

looks like a temporary file problem
how does macos handle these?

[AndreaGuarracino]

It seems macos does not like stepindex:

odgi test is a Catch v2.13.7 host application.
Run with -? for options

-------------------------------------------------------------------------------
step index construction, and position retrieval.
  The index can be saved and loaded. After loading, we can retrieve all the
  correct positions again.
-------------------------------------------------------------------------------
/Users/runner/work/odgi/odgi/src/unittest/stepindex.cpp:654
...............................................................................

/Users/runner/work/odgi/odgi/src/unittest/stepindex.cpp:654: FAILED:
due to unexpected exception with message:
  [odgi::algorithms::stepindex] error: SDSL step index file does not have