Github Action’s MacOS runners support virtualization with virtualbox. This could be used to add CI for more platforms.
I’ve tried vmactions/freebsd-vm action to run specs in a FreeBSD VM. It technically works. But it’s excrutiatingly slow 
The job test_freebsd gets cancelled after the maximum runtime of 6 hours. By then it had only completed maybe 2/3 of std_spec.
It feels like it shouldn’t be that slow. I couldn’t find any specifics on the virtualization strategy, though.
Just wanted to post this, maybe it can be investigated further at some point.