Is your feature request related to a problem? Please describe.
I'm annoyed at the awkward situation that I have to receive emails about the failing pipelines: You are unable to write a change note until you creates the PR, when the PR number is available. So I'm sure to receive an email about a failing pipeline the first time I creates a PR.

Describe the solution you'd like
The pipeline should not fail if the change note is missing. It may fail if the there exists format error in the change note.
Just like a missing CLA doesn't make the pipeline fail.