cicd: prevent creating multiple jobs on merge requests

cicd/gitlab-ci.yml

@@ -9,6 +9,10 @@ variables:
 
 workflow:
   name: 'Qt-${QDS_CI_QT_VERSION} - ${CI_COMMIT_MESSAGE}'
+  rules:
+    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
+    - if: '$CI_COMMIT_BRANCH && $CI_OPEN_MERGE_REQUESTS'
+      when: never
 
 stages:
   - build