Use goreleaser-cross container img for gh release workflow

[spwoodcock]

• Following on from Add config to generate binaries for the build cmd line tool #30
• This time the workflow has been verified to work on my fork: https://github.com/spwoodcock/go-tilepacks/actions/runs/11942875622/job/33290792326
  • See the final release and binaries here: https://github.com/spwoodcock/go-tilepacks/releases/tag/0.1.0
• I was a bit hasty ready the failed workflow logs: https://github.com/tilezen/go-tilepacks/actions/runs/11872649486/job/33086593280 and commenting on the PR. The issue isn't to do with Android at all. It's missing gcc and gcc binaries for most platforms...
• The solution was to move away from the typical Goreleaser Github action & instead use the goreleaser-cross image manually.
• The container image contains all required dependencies for cross compiling, making it really simple.

Note: I also updated the workflow to run only on release, as goreleaser needs a release to attach the built binaries to.