Add tests for runner execution on FreeBSD

We currently have no tests executing the runner inside a FreeBSD environment.

This issue replaces gitlab-org/quality/testcases#163 (closed)

As this is different kernel type entirely we can't do this inside docker (at least without some additional hacks I'm unaware of).

One, heavy, option would be to use xhyve inside a shared Mac runner and launch a FreeBSD VM inside there. That's a lot of heavy lifting to exercise this relatively low risk, low use scenario though.