Changed setting the architecture for Alpine to also work for arm64

[malice00]

This fixes #3616 by not having the architecture hardcoded to x64-musl, but instead appending the -musl part to the architecture that was already found.
I am unable to supply tests, since the tarball I want to have loaded only exists on a private server. But the existing alpine-test should still work -- couldn't test this because the test would generally not run on my machine, probably because I am generally using nvm.

[ljharb]

Are you saying that there's no publicly available node distribution for this use case?

[malice00]

Only the x64 version on node's unofficial-project.

Project: https://github.com/nodejs/unofficial-builds
Tarballs: https://unofficial-builds.nodejs.org/

[malice00]

So, we decided to make our builds publicly available. Still not sure on how to add a test, but local testing works with this URL: https://raw.githubusercontent.com/appthreat/nodejs-unofficial-builds/master/dists/. Currently it only contains v24.3.0 for both alpine arm64 and x64.