Ensure no-selinux case is at least e2e tested periodically

[cgwalters]

This issue tracks our "full" support for installing SELinux-enabled targets from SELinux-disabled hosts.

[albertofaria]

FWIW, crun-vm will make use of this as part of its support for running bootc containers.

[larsks]

Running a bootc build (on a Fedora 40 system)...

root@host:~# podman run \
  --rm \
  -it \
  --privileged \
  --pull=newer \
  --security-opt label=type:unconfined_t \
  -v "$PWD/output:/output" \
  -v /var/lib/containers/storage:/var/lib/containers/storage \
  registry.redhat.io/rhel9/bootc-image-builder:latest \
  --type qcow2 \
  --local \
  bootc-test-image

...I was directed here by this warning:

Host kernel does not have SELinux support, but target enables it by default; this is less well tested.  See https://github.com/containers/bootc/issues/419

And yet selinux is both present and enabled on the host:

root@host:~# getenforce
Enforcing

What's going on here?

(NB: I see the same message using quay.io/centos-bootc/bootc-image-builder:latest)

[cgwalters]

PR in #790