CI: explicitly set expected image type
In case the systemwide default image changes, set the desired image explicitly.
In fact, the default did recently change from ubuntu:bionic
to suse-qt66:latest
from the local invent-registry.kde.org/sysadmin/ci-images
registry. This of course contains no apt-get
command, and ubuntu:bionic
is out-of-support by now. So start using ubuntu:22.04
now.