Token selection logic is not good

[doronbehar]

For the first time I ran goreleaser, I encountered this very unclear error message:

   • building...
   • loading config file       file=.goreleaser.yml
   • loading environment variables
   ⨯ build failed after 0.00s error=multiple tokens defined. Only one is allowed

And I didn't understand what's wrong with my configuration file. Apparently, after reading the source code I read this:

https://github.com/goreleaser/goreleaser/blob/main/internal/pipe/env/env.go#L81-L104

And I realized that I have to unset one of my GIT{LA,HU}B_TOKEN environment variables, which are both set by default in my shell rc files.

I think the error message could at least be improved, or you can default to the GitHub token?

[caarlos0]

should be better after #2733

Thanks!