citemplate: also check the forked registry for image builds

citemplate: also check the forked registry for image builds

In case you are developing a set of changes in a module, in
conjunction with a branch in gst-ci, you will end up with
a template with a different tag than the upstream repo, which
will be refferencing your gst-ci forked registry.

But that image won't existin in the namespace the
module would be running at, so we need to copy it from there.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-ci/-/merge_requests/308>