Node.js unofficial-builds publishes linux-arm64-musl binaries since v20.20.1 / v22.21.1 / v24+.
Map NVM_ARCH=arm64 to arm64-musl on Alpine so `nvm install`
resolves to the correct tarball instead of the glibc-linked arm64 build that won't run against musl.
[Tests] `nvm_get_arch`: expect arm64-musl on Alpine
Co-authored-by: Jesse Zhu <jesse@itjesse.com>
Co-authored-by: Jordan Harband <ljharb@gmail.com>
