[CI] Add token permissions for add-ready-label CI job (vllm-project#17730)

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>
Signed-off-by: Yuqi Zhang <[email protected]>

Author: 2 people

.github/workflows/add_label_automerge.yml

@@ -1,4 +1,6 @@
 name: Add label on auto-merge enabled
+permissions:
+    issues: write
 on:
     pull_request_target:
         types: