ci: add permission of write for security-events for dependabot.

Signed-off-by: Lan Liang <gcslyp@gmail.com>

.github/workflows/ci-image-scanning.yaml

@@ -5,6 +5,8 @@ jobs:
   use-trivy-to-scan-image:
     name: image-scanning
     if: ${{ github.repository == 'karmada-io/karmada' }}
+    permissions:
+      security-events: write
     runs-on: ubuntu-22.04
     strategy:
       fail-fast: false