Use 'rules' in '.gitlab/ci/cng.gitlab-ci.yml'

Signed-off-by: Rémy Coutable <remy@rymai.me>

.gitlab/ci/cng.gitlab-ci.yml

+# Make sure to update all the similar conditions in other CI config files if you modify these conditions
+.if-canonical-gitlab-tag: &if-canonical-gitlab-tag
+  if: '$CI_SERVER_HOST == "gitlab.com" && $CI_PROJECT_NAMESPACE =~ /^gitlab-org($|\/)/ && $CI_COMMIT_TAG'
+
 cloud-native-image:
-  extends: .only:variables-canonical-dot-com
   image: ruby:2.6-alpine
   dependencies: []
   stage: post-test
   allow_failure: true
   variables:
     GIT_DEPTH: "1"
-  when: manual
   script:
     - install_gitlab_gem
     - CNG_PROJECT_PATH="gitlab-org/build/CNG" BUILD_TRIGGER_TOKEN=$CI_JOB_TOKEN ./scripts/trigger-build cng
-  only:
-    refs:
-      - tags
+  rules:
+    - <<: *if-canonical-gitlab-tag
+      when: manual