downgrade alpine used for reproducible builds
temporary fix for #1335
so far on my quest I've found that the issue happens while building llvm for tapi, which we get from some 3rd party.
The error we get happens because of a change in musl, which caused a compilation problem with llvm, which has been fixed since.
Apple distributes a more recent version of tapi, but i haven't been able to get it to work with our current tooling yet. It probably pulls a more recent version of llvm which is hopefully free of that issue. Otherwise i'm not sure what our course of action will be.