Update build.yml to build for amd64 and arm64

[ckuhtz]

I have not tested this, but this should be accurate or mostly accurate as an example for what the github issue is requesting.

[mkasberg]

I think the concept here will work.

I have a hunch that the docker/setup-qemu-action will require our build to be in Docker. I haven't confirmed this, I need to read more docs. If the build does need to be in Docker, that's possible, I prototyped it in #2 but was on the fence about if that was the right approach. Seems like it is a better approach if it unlocks builds on more architectures for us. (I might need to update/rebase that old PR for recent changes in main.)