First attempt at GitHub action to ensure release note entry included in PRs.

.github/workflows/pr_release_note_entry.yml

@@ -0,0 +1,17 @@
+name: 'Check PR Release Note Entry'
+
+on:
+  pull_request:
+    branches:
+      - main
+    tags-ignore:
+      - '*.*'  # ignore releases
+
+jobs:
+  release-note-entry:
+    name: 'Checking release note entry for PR ${{ github.event.number }}'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - run: |
+          test -f './newsfragments/${{ github.event.number }}.*'