FWIW, every commit for the Go project is tested on multiple 32-bit architectures, including pre-commit tests and post-commit tests.

You can see a list here:

https://build.golang.org/

(That particular build dashboard just shows post-commit tests. '386' there is 32-bit x86, 'arm' is 32-bit ARM.)

I can't speak to what Google runs in production or what Google tests internally, but the Google-run CI for the Go project definitely does test 32-bit, and those tests essentially match the tests run against 64-bit.