gitlab-CI: Enable arm64 test target

Our gitlab no supports binfmt-misc running of forgein binaries:

freedesktop/freedesktop#91

Only thing missing is that we also need to install qemu-user-static,
since binfmt-misc wants to run that binary from our namespace.

Big kudos to Daniel for setting this up.

Example run on my stuff branch:

https://gitlab.freedesktop.org/danvet/igt-gpu-tools/-/jobs/50307



Cc: Daniel Stone <daniel@fooishbar.org>
Reviewed-by: Sean Paul <sean@poorly.run>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>