Test suite: work towards CI via GitHub Actions

[jgehrcke]

A zero-to-one effort that's probably more realistically targeted as a zero-to-pointfive effort. Adding value while knowingly cutting some corners.

Test ComputeDomains in an environment that supports IMEX / NVLink. Tthat’s a challenge w.r.t.

• getting runners set up
• getting an environment to run in at all
• getting decent job concurrency
• job isolation
• security
• ...

We need to be ready to cut corners, and get going -- to learn what really to focus on.