ci: Use the CI image produced by the pipeline

The newly-added eslint_mr job still uses the manually built
extension image instead of the image that is built as part
of the pipeline.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1504>

.gitlab-ci.yml

@@ -100,7 +100,9 @@ eslint:
         when: always
 
 eslint_mr:
-    image: registry.gitlab.gnome.org/gnome/gnome-shell/extension-ci:v2
+    extends:
+        - .fdo.distribution-image@fedora
+        - .gnome-shell.fedora:33
     stage: review
     script:
         - export NODE_PATH=$(npm root -g)