set default changelog messages to fail the changelog CI

.github/workflows/clippy_changelog.yml

@@ -26,8 +26,8 @@ jobs:
       run: |
         body=$(curl -H "Authorization: token ${{ secrets.GITHUB_TOKEN }}" -s "https://api.github.com/repos/rust-lang/rust-clippy/pulls/$PR_NUMBER" | \
           python -c "import sys, json; print(json.load(sys.stdin)['body'])")
-        output=$(grep "^changelog:\s*\S" <<< "$body" | sed "s/changelog:\s*//g") || {
-          echo "ERROR: pull request message must contain 'changelog: ...'. Please add it."
+        output=$(grep "awk '/^changelog:\s*\S/ && !/changelog: \[.*\]: your change/' <<< "$body" | sed "s/changelog:\s*//g") || {
+          echo "ERROR: pull request message must contain 'changelog: ...' with your changelog. Please add it."
           exit 1
         }
         echo "changelog: $output"