title: Azure Devops build pipeline: CI triggers not working on PR merge to master when PR set to none
body: <p>Need to trigger CI build job when a PR is merged to master (only when change is inside ./rel/* path) but not have CI build triggered when the Pull Request (PR) is created. So I have the trigger config as below.</p>
  
  <pre><code>trigger:
      branches:
          include:
          - master
      paths:
          include:
          - ./rel/*
  
  pr: none # will disable PR builds (but not CI builds)
  </code></pre>
  
  <p>But it fails to trigger CI build when <code>pr: none</code> is added. If <code>pr: none</code> is removed, The Job is getting triggered for both PR and a merge to master. I would only need the job/CI build to run on a merge to master.</p>