Add 32-bit builds to GitHub Actions CI

[esabol]

Ideally, we should add 32-bit builds to the GitHub Actions CI to prevent problems with 32-bit architectures from creeping into the source code in the future.

https://dev.to/drhyde/automatic-cross-platform-testing-part-6-32-bit-linux-fh2 - this method no longer works

[esabol]

Need to do the 32-bit builds in a Docker container, I think. Would 32-bit Alpine work?

https://github.com/marketplace/actions/setup-alpine-linux-environment