Built releases for OpenBSD

[GideonBear]

Checklist

• I have searched the issue tracker for relevant or duplicate issues.

I want to suggest some general feature

Topgrade should build release assets for OpenBSD.

I'm open to building for OpenBSD using something like vmactions/openbsd-vm. We don't necessarily need to add it in CI, if it fails to build there, we can fix it in the next release.

Ref #1581, ping @Izder456

[Izder456]

Might be useful as a reference: I wrote some CI for the https://github.com/melonDS-emu/melonDS project building Binaries for OpenBSD which was later expanded upon for building FreeBSD and NetBSD binaries by another contributor @GideonBear