ci(gitlab-ci): uses $CI_OPEN_MERGE_REQUESTS in workflow since heptapod has been updated

.gitlab-ci.yml

@@ -6,7 +6,7 @@ image: python:latest
 workflow:
   rules:
     - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
-    - if: '$CI_COMMIT_REF_NAME =~ /^topic\/.*/'
+    - if: '$CI_COMMIT_REF_NAME =~ /^topic\/.*/  && $CI_OPEN_MERGE_REQUESTS'
       when: never
     - when: always