workflows: don't jumpstart the flatpak test
workflows: don't jumpstart the flatpak test

We have node in the default image already, and building it ourselves is
actually faster than waiting for and downloading it.

At some point we might chain our workflows to depend on each other and
then it might make sense to bring this back.

cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,martinpitt/cockpit,mvollmer/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,cockpit-project/cockpit