title: GitLab CI: MERGE_REQUEST_EVENT not triggered by update?
body: <p>I'm testing GitLab CI pipelines.</p>
  <p>I have created a merge request named &quot;TEST&quot; that have its <code>gitlab-ci.yml</code> with a rule like below:</p>
  <pre class="lang-yaml prettyprint-override"><code>if '$CI_PIPELINE_SOURCE == &quot;merge_request_event&quot; &amp;&amp; $CI_MERGE_REQUEST_TITLE == &quot;TEST&quot;'
  </code></pre>
  <p>It worked fine as I expected. Create event triggered the <code>merge_request_event</code>.<br />
  However, if I create a merge request have another title and then I update it to &quot;TEST&quot;, It doesn't seems to trigger the <code>merge_request_event</code>.</p>
  <p>According to <a href="https://docs.gitlab.com/ee/ci/jobs/job_control.html" rel="nofollow noreferrer">this document</a>, <code>merge_request_event</code> is supposed to be triggered by updated too.</p>
  <blockquote>
  <p>For pipelines created when a merge request is created or updated. Required to enable merge request pipelines, merged results pipelines, and merge trains.</p>
  </blockquote>
  <p>Do I take it wrong or missed important information or documents?</p>