tests: Port `jobserver-error` to rmake.rs
Part of #121876.
This PR ports `tests/run-make/jobserver-error` to rmake.rs, and is basically #128789 slightly adjusted.
The complexity involved here is mostly how to get `/dev/null/` piping to fd 3 working with std `Command`, whereas with a shell this is much easier (as is evident with the `Makefile` version).
Supersedes #128789.
This PR is co-authored with `@Oneirical` and `@coolreader18.`
try-job: aarch64-gnu
try-job: i686-gnu-1
try-job: x86_64-gnu-debug
try-job: x86_64-gnu-llvm-18-1
cf577f34c4