Set up macOS tests on self-hosted runner

[Tackx]

No objections to the re-assignment, especially since soon I'll be going on vacation and I won't have the capacity to work on this.

Let me add that since we're currently focusing a bit more on macOS then we really should try to include a pipeline for darwin in our self-hosted runner. Perhaps we can use something like Docker-OSX.
All in the name of our security research of course.

Originally posted by @krixlion in #35