title: Jenkins: Github webhook does not trigger any job
body: <p>I try to configure Jenkins. I want a simple behavior: trigger a build on new pull request.</p>
  
  <p>I cannot understand what I missed...</p>
  
  <p>Jenkins version: 2.89.2</p>
  
  <p><strong>At <a href="https://ci.mysite.fr/configure" rel="noreferrer">https://ci.mysite.fr/configure</a> :</strong></p>
  
  <p><a href="https://i.stack.imgur.com/woQHZ.png" rel="noreferrer"><img src="https://i.stack.imgur.com/woQHZ.png" alt="enter image description here"></a></p>
  
  <p><strong>Still no build triggered:</strong></p>
  
  <p><a href="https://i.stack.imgur.com/WonXK.png" rel="noreferrer"><img src="https://i.stack.imgur.com/WonXK.png" alt="enter image description here"></a></p>
  
  <p><strong>At <a href="https://ci.mysite.fr/job/test-back/configure" rel="noreferrer">https://ci.mysite.fr/job/test-back/configure</a> :</strong>
  <a href="https://i.stack.imgur.com/a55Oc.png" rel="noreferrer"><img src="https://i.stack.imgur.com/a55Oc.png" alt="enter image description here"></a></p>
  
  <p><strong>On Github, Webhook is sent and well received by Jenkins:</strong></p>
  
  <p><a href="https://i.stack.imgur.com/WICdj.png" rel="noreferrer"><img src="https://i.stack.imgur.com/WICdj.png" alt="enter image description here"></a></p>
  
  <p><strong>Nginx Log says the same:</strong></p>
  
  <p><a href="https://i.stack.imgur.com/NYi8z.png" rel="noreferrer"><img src="https://i.stack.imgur.com/NYi8z.png" alt="enter image description here"></a></p>
  
  <p>Help please!</p>