CI: run tests on macOS

TODO

• minimal example of running macOS jobs. The cloud that powers these are "M1" (arm64) macs.
• get python working
  • there are more than one python: python3 is from homebrew, it is specific to arm46 architecture. It is in /opt/homebrew/opt/python@3.10/libexec/bin/python and comes that way in the provided CI image (from GitLab).
  • there is also /usr/bin/python3: I think this ships with the OS and is a "fat binary".
  • its also possible to install a specific latest version if python: /usr/local/bin/python3 which has some advantages and is also a "fat binary".
• ensure make is available.
• install octave
  • maybe from homebrew?
• build Pythonic
  • determine if any of the above Pythons have enough of the --shared-library for Pythonic to work
• get GNU Sed via brew and use SED=gsed during macOS testing.
• remove allowed-to-fail
• tests run: some tests passing
• most tests passing
• all tests passing
• would caching /opt/homebrew allow for faster CI runs?
  • future work: I think one would need to configure homebrew to install in the local dir instead of /opt/homebrew.
  • current job run time is around 13 mins, so not sure its worth the effort.