ci: Update container image URL

The container image used for CI is now built from a project in the
gitlab.gnome.org/GNOME/ namespace, rather than my personal namespace.

.gitlab-ci.yml

@@ -6,7 +6,7 @@ stages:
 
 test-fedora-latest:
   stage: test
-  image: registry.gitlab.gnome.org/sthursfield/tracker-oci-images/amd64/fedora:latest
+  image: registry.gitlab.gnome.org/gnome/tracker-oci-images/amd64/fedora:latest
 
   script:
     # We can build and test tracker-miners against tracker just by building