Use 'stable' for go versions in github actions

[robdimsdale]

According to the setup-go action documentation, we can use:

  - uses: actions/setup-go@v4
    with:
      go-version: 'stable'

Instead of hard-coding a version of go and having to change that every few months when the versions of golang update.

I don't see a reason not to use stable. We want the buildpacks to be built with the latest stable; we don't need to validate that the buildpacks are able to be built with older versions of golang.

For libraries (e.g. packit, libnodejs, etc), we could expand this to a matrix support, consisting of stable and oldstable if we wanted to validate that the libraries still work fine on all supported versions of golang.