Container package tests not validating cross architecture mappings in MRs

When submitting a MR that impacts the mappings.yml file, we run a bunch of jobs to validate the package mappings on every distro. We're only doing this for the x86_64 architecture though, and thus missing coverage of package mappings for all other Debian architectures and for the Fedora mingw package set. This is highly likely to allow through mapping bugs, or cause us to miss when a distro discontinues an architecture.

eg Debian recently-ish dropped mipsel. The riscv64 arch is also currently broken since it is transitioning from a separate port, to an official arch (qemu-project/qemu#1883 (closed)).