Take 2 of https://github.com/Homebrew/brew/pull/17692 but with:
- provide and document `HOMEBREW_NO_VERIFY_ATTESTATIONS`
- don't try to run unless there's GitHub credentials
- don't try to run unless `gh` is installed
- don't try to run in CI
While we're here:
- split out a `Homebrew::EnvConfig.devcmdrun?` helper method
- add some missing `Homebrew::EnvConfig.github_api_token` presence
checks
b8ff4b3d23