GREP for PR reference accepts references that are split over a line (#…

…2072)

Fixes #2070

.github/workflows/changelog.yml

@@ -16,6 +16,6 @@ jobs:
       - name: Grep CHANGES.md for PR number
         if: contains(github.event.pull_request.labels.*.name, 'skip news') != true
         run: |
-          grep -P "PR #${{ github.event.pull_request.number }}[^0-9]" CHANGES.md || \
+          grep -Pz "PR( |\n\s*)#${{ github.event.pull_request.number }}[^0-9]" CHANGES.md || \
           (echo "Please add 'PR #${{ github.event.pull_request.number }}' change line to CHANGES.md" && \
           exit 1)