macos-15-arm64 detected as self-hosted

[jvanderwee]

Ensure the following before filing this issue

• I verified it reproduces with the latest version with - uses: ruby/setup-ruby@v1 (see Versioning policy)

• I tried to reproduce the issue locally by following the workflow steps (including all commands done by ruby/setup-ruby, except for Downloading Ruby & Extracting Ruby),
  and it did not reproduce locally (if it does reproduce locally, it's not a ruby/setup-ruby issue)

Are you running on a GitHub-hosted runner or a self-hosted runner?

GitHub-hosted runner

Link to the failed workflow job (must be a public workflow job, so the necessary information is available)

N/A

Any other notes?

macOS 15 images just released: https://github.com/actions/runner-images/releases/tag/macos-15%2F20240923.103

[eregon]

Right, it's listed at https://docs.github.com/en/actions/using-github-hosted-runners/using-github-hosted-runners/about-github-hosted-runners#supported-runners-and-hardware-resources as in Beta now.

I think we can just use the existing Ruby builds from older macOS versions. Maybe even relax to allow any version >= the version we build on.