title: Run Github Actions when pull requests have a specific label
body: <p>After reading the documentation of the <a href="https://help.github.com/en/actions/reference/events-that-trigger-workflows#pull-request-event-pull_request" rel="noreferrer">Events that trigger workflows</a>, I wonder if it's possible to run a workflow with a <strong>given label name</strong>, like RFR or WIP.  </p>
  
  <p>I know we can run a workflow when the pull request is labeled, but there is nothing more for a specifc label name :</p>
  
  <pre><code>on:
    pull_request:
      types: [labeled]
  </code></pre>
  
  <p>Has anyone done this before ?</p>