ci: add workflow to restrict direct PRs to release branches (#8240)

.github/workflows/release-pr-check.yaml

@@ -0,0 +1,19 @@
+name: Backport PR Check
+
+on:
+  pull_request:
+    branches:
+      - 'release/v*'
+
+jobs:
+  check-pr-author:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check PR author
+        id: check_author
+        run: |
+          if [ "${{ github.actor }}" != "aqua-bot" ]; then
+            echo "::error::This branch is intended for automated backporting by bot. Please refer to the documentation:"
+            echo "::error::https://trivy.dev/latest/community/maintainer/backporting/"
+            exit 1
+          fi