test: Remove cockpit/ws container on non-coreos images

In cockpit-project/bots#7046 we want to
pre-install the cockpit/ws container to the fedora-40 image (and in the
future, whichever Fedora version the container is based on). This
"breaks" pixel tests due to the additional container image, so remove it
for anything except fedora-coreos.

We don't just want to include it in the pixel tests, as the container's
base image and pixel reference OS move independently.

test/vm.install

@@ -37,6 +37,9 @@ fi
 # Since 4.0 podman now ships the pause image
 podman images --format '{{.Repository}}:{{.Tag}}' | grep -Ev 'localhost/test-|pause|cockpit/ws' | xargs -r podman rmi -f
 
+# clean up cockpit/ws on Fedora images, as it "breaks" pixel tests; it's only relevant for CoreOS
+[ "$1" = "fedora-coreos" ] || podman rmi -f quay.io/cockpit/ws || true
+
 # tests reset podman, save the images
 mkdir -p /var/lib/test-images
 for img in $(podman images --format '{{.Repository}}:{{.Tag}}'); do