Get testing system off Travis

[zorbathut]

We used to use Travis's free service in order to test the code via a VM. Unfortunately, Travis took its free service out behind the barn a few months back.

I've been using Github Actions for a lot of my personal testing and it's pretty good . . . but they say the Linux environment doesn't support VMs. So, a few options to be evaluated:

• Figure out how to get testing VMs on their Linux environment anyway (this is probably a dead end)
• Figure out how to get testing working without a VM (this sounds impractical to me)
• Figure out how to get testing VMs working on their Mac environment (this seems like a waste, mac is much more "expensive", but it's free for open-source projects, so, whatever, their loss)
• Find a new free service that supports VMs, get it working there
• Find a paid service that supports VMs, evaluate expected cost (I guess we could just use Travis)

Someone's gotta dive through these and find a sensible solution.

[zorbathut]

"Figure out how to get testing VMs working on their Mac environment" - see https://github.com/jonashackt/vagrant-github-actions