CI: find a way to get GPUs tested in CI

[tylerjereddy]

This is a bit painful, but probably useful eventually. I think Kokkos core has/had a way to do this.

Most likely the biggest pain point is that you'd need self-hosted runners, which almost always end up being more of a maintenance burden than they are worth. It would be great if there were an actual external service provider for this. May want to scan some of the large GPU-capable OSS Python projects to see what they do as well.