Use docker/setup-qemu-action

[radarhere]

In January, the ppc64le and s390x jobs started experiencing segfaults. We downgraded the hosts to Ubuntu 22 in #8713, but the segfaults have started happening again since then. I presumed a fix would eventually occur upstream, but it's been a while and we're approaching a release.

This is a suggestion to switch from

docker run --rm --privileged aptman/qus -s -- -p ${{ matrix.qemu-arch }}

to https://github.com/docker/setup-qemu-action

• Seems simpler
• Fixes the segfaults
• We can revert the temporary downgrading of the hosts

[hugovk]

Good stuff, thanks!