I currently have a task that I intend to run only once when a PR is created. Any pipeline runs due to new commits should not trigger the task. I was wondering if there is a way to detect the runs triggered by changes to code in the PR? When I use the predefined variable $(Build.Reason) I get back PullRequest for both builds(One triggered when PR is created and other when updates are made to PR).

This is what I have in my pipeline and I have enabled build validation for my pipeline.

trigger:
- master
pr:
- master