That's great. I hope it works out, and you have CI for NetBSD, OpenBSD, and illumos, too.
Go's support for NetBSD has been a big boon to the more casual NetBSD user who isn't going to maintain a port. It means a random Go open-source project you use probably works on NetBSD already, or if it doesn't, it can be fixed upstream. Maybe Zig could play a similar role.
It's a shame GitHub doesn't have native CI even for FreeBSD on x86-64. I can see the economic case against it, of course. That said, the third-party Cross-Platform GitHub Action (https://github.com/cross-platform-actions/action) has made Free/Net/OpenBSD CI practical for me. I have used it in many projects. The developer is currently working on OmniOS support in https://github.com/cross-platform-actions/omnios-builder.