fix: pin musl 1.2.5 for DNS fixes (#6189)

## Summary
musl 1.2.5 includes [several fixes to DNS over
TCP](https://www.openwall.com/lists/musl/2024/03/01/2), which appears to
be the root cause of #6116.

This approach is a bit janky, but according to codex:
> On the Ubuntu 24.04 runners we use, apt-cache policy musl-tools shows
only the distro build (1.2.4-2ubuntu2)"

We should build with this version and confirm.

## Testing
- [ ] TODO: test and see if this fixes Azure issues