Check newsfragments using a custom Action

.github/workflows/check-newsfragment.yml

@@ -0,0 +1,23 @@
+name: Check newsfragment
+
+on:
+  pull_request:
+    types: [labeled, unlabeled, opened, closed, synchronize]
+    branches:
+    - main
+
+jobs:
+  check-newsfragment:
+    if: ${{ !contains(github.event.pull_request.labels.*.name, 'skip newsfragment') }}
+    runs-on: 'ubuntu-latest'
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Check newsfragments
+        run: |
+          if git diff --name-only origin/main | grep -v '/_tests/' | grep 'src/trio/'; then
+            git diff --name-only origin/main | grep 'newsfragments/' || exit 1
+          fi