Really don't run diff-pr on label changes
Really don't run diff-pr on label changes

We need to be able to filter out changes other than "allow breaking
changes" in the trigger - doing it in the "if" is too late, as:

- it comes after permissions, so the CLA bot still triggers it
- it ends up causing the check to show as skipped, rather than just not triggering it

jskeet/google-cloud-dotnet,jskeet/google-cloud-dotnet,jskeet/gcloud-dotnet,jskeet/google-cloud-dotnet,jskeet/google-cloud-dotnet,jskeet/google-cloud-dotnet,googleapis/google-cloud-dotnet,googleapis/google-cloud-dotnet,googleapis/google-cloud-dotnet