Update lock.yml permissions

Signed-off-by: NJoyce <joycebrum@google.com>

.github/workflows/lock.yml

@@ -4,9 +4,14 @@ on:
   schedule:
     - cron: '0 0 * * *'
 
+permissions: {}
+
 jobs:
   lock:
     runs-on: ubuntu-latest
+    permissions:
+      issues: write
+      pull-requests: write
     steps:
       - uses: dessant/lock-threads@v2
         with: