title: How to get pull request number within GitHub Actions workflow
body: <p>I want to access the Pull Request number in a Github Actions workflow. I can access the GITHUB_REF environment variable that is available. Although on a Pull Request action it has the value: "refs/pull/125/merge". I need to extract just the "125". </p>
  
  <p>I have found a similar post <a href="https://stackoverflow.com/questions/58033366/how-to-get-current-branch-within-github-actions">here</a> that shows how to get the current branch using this variable. Although in this case, what I am parsing is different and I have been unable to isolate the Pull Request number. </p>
  
  <p>I have tried using {GITHUB_REF##*/} which resolves to "merge" 
  I have also tried {GITHUB_REF#*/} which resolves to "pull/125/merge"</p>
  
  <p>I only need the Pull Request number (which in my example is 125)</p>