ci: Disable container building temporarily

The freedesktop.org GitLab is undergoing extensive migration, so to
unblock our CI, disable container building using ci-templates for now.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/4337>

.gitlab-ci.yml

@@ -326,9 +326,14 @@ check-merge-request:
   rules:
     - !reference [.only-merge-requests, rules]
 
+.dummy-container-build:
+  script:
+    - echo Dummy container build
+
 build-fedora-container@x86_64:
   extends:
-    - .fdo.container-build@fedora@x86_64
+    #- .fdo.container-build@fedora@x86_64
+    - .dummy-container-build
     - .mutter.fedora@x86_64
     - .mutter.skip-git-clone
   stage: prepare
@@ -337,7 +342,8 @@ build-fedora-container@x86_64:
 
 build-fedora-container@aarch64:
   extends:
-    - .fdo.container-build@fedora@aarch64
+    #- .fdo.container-build@fedora@aarch64
+    - .dummy-container-build
     - .mutter.fedora@aarch64
     - .mutter.skip-git-clone
   stage: prepare