Switch building Linux arm64 launchers to a GitHub-hosted runner

[Gedochao]

Seems like we can't switch building the Linux arm64 launchers to a github launcher for now, as the MacOS aarch64 runners don't have access to docker.
actions/runner-images#9254 (comment)

The hope in that matter is twofold:

• this might be solved in a future macos-15 or higher runner, if the underlying hardware was M3 or newer (GitHub Action: New M1 runner available to all plans, including open source 🚀 actions/runner-images#9254 (comment))
  • https://developer.apple.com/documentation/virtualization/vzgenericplatformconfiguration/4360553-isnestedvirtualizationsupported?changes=latest_minor
• the more likely solution is when Linux arm64 runners get out of public beta and become available for open source projects (which is uncertain on the if and when, but they're currently in public beta: https://github.blog/changelog/2024-06-03-actions-arm-based-linux-and-windows-runners-are-now-in-public-beta/)

Still, it's a clear improvement to be able to run MacOS aarch64 tests on every PR, rather than just on main, so that part still seems worth doing here.

Originally posted by @Gedochao in #3050 (comment)

• migrate to GitHub runners in scala-cli jobs
• migrate coursier-m1 back to the coursier main repo

[Gedochao]

(extracted out of #2936)