ci: test goreleaser setup

[myitcv]

Depends on goreleaser/goreleaser#2355. Ideally we want to add a step to at least one entry in the regular build matrix (but perhaps not all because it will add time) to dry-run the goreleaser setup. Per goreleaser/goreleaser#2355 (comment), it would be ideal if we could assert the behaviour against some sort of golden file.

cc @caarlos0

[mvdan]

I tihnk @myitcv and I did this in https://review.gerrithub.io/c/cue-lang/cue/+/549190 - pushes to branches now run goreleaser in "snapshot" mode, until something like goreleaser test is supported by upstream. I think we could close this issue on our side, and watch goreleaser/goreleaser#2355 to consider switching to that when available?

[mvdan]

^ Doing the above. I will send a tiny CL to link to the upstream issue via a TODO, however, as I think keeping a small reminder with a link is best. I don't think we need to keep this issue open, as the goreleaser setup is being tested well enough now.