Separate musl and libc linux builds in CI (#10830)
We have a lot of jobs downstream of the `build-binary-linux` job, but
the job is significantly slower than the other binary builds because we
need to configure musl. Instead, we split this into two jobs (as it was
before https://github.com/astral-sh/uv/pull/2309#discussion_r1520101330)
to speed things up.
The libc job takes ~1m and its _downstream_ jobs finish before the musl
build does. The musl job takes ~5m.
