Migrate the CI Arm64 Build to the new GitHub Arm-based Linux runners (when available)

[laurenceisla]

According to this recent announcement, there are new Arm-based Linux runners for CI available: https://github.com/actions/partner-runner-images.

Unfortunately, for now, there are two big caveats:

• Open Source projects cannot use these runners until the end of the year. Only available for Teams and Enterprise plans.
• They don't support Haskell by default. We need to install it and configure manually (maybe with GHCup like in the amd64 runners or our remote arm64 server).

In the meantime we could still use the self-hosted image that is being worked in #3540.

[steve-chavez]

Only available for Teams and Enterprise plans.

We could subscribe to Team plans. Would that bring an advantage over our self hosted runners?

[laurenceisla]

We could subscribe to Team plans. Would that bring an advantage over our self hosted runners?

Not really sure, since the self host isn't implemented yet and we cannot test if the Haskell builds in arm runners are feasible right now (I'm thinking that it shouldn't be too difficult, but still, not sure). So a cost / benefit comparison can't be done yet.