Add a workaround for the issue that podman falls back to the 'cni'
network backend when finding any container images in the local storage
when executed for the first time. Since we started embedding container
images in our CI runner images, this resulted in failures, because the
OS is missing some required CNI plugins. Until we somehow fix this in
osbuild, we explicitly set the network backend to 'netavark'.
This is relevant only for RHEL-9 / c9s, because Fedora since F40 and
el10 support only `netavark` backend.
Signed-off-by: Tomáš Hozza <thozza@redhat.com>
987da06136