Add CI for non-x86 architectures

[mbeutel]

We occasionally run into issues which surface only on non-x86 architectures (e.g. #337, #304). Perhaps we can add some CI for some of these architectures?

One way of approaching this might be to use GitHub Actions with the Run-on-Arch action, which makes use of QEMU to simulate other architectures. As always I'm open to other suggestions and PRs.