[tlbuild] TeX Live builds via Github - Solaris done

[Mojca Miklavec]

> Darwin-legacy requires a very old OS that isn't supported via GitHub
> actions, so I'm not sure how to do that, even though it would be
> awesome if there was a way.

... and Darwin requires some signing and notarizing. If you just want
to test if it builds, you could already do so.
Last time I checked, Arm wasn't supported yet, but it was on the roadmap.

Mojca