title: How to write .gitlab-ci.yml job to run only in merge-request
body: <p>How to right write job in .gitlab-ci.yml when it run only in  merge requests?</p>
  
  <pre><code>test_c:
    stage: test
    script:
      - echo "This job tests something. It will only run when all jobs in the"
      - echo "build stage are complete."
    only:
      - merge_requests
  </code></pre>
  
  <p>This job not run in merge request, but not run and in commint in master or develop.</p>