fix(CI): Update assign-reviewers.yml

Author: jmulcahey-twilio

.github/workflows/assign-reviewers.yml

@@ -2,7 +2,21 @@ name: Assign Reviewers
 
 on:
   pull_request_target:
-    types: [opened, ready_for_review, reopened, synchronize, labeled, unlabeled]
+    branches:
+      - main
+    types:
+      - ready_for_review
+      - synchronize
+
+permissions:
+  actions: read
+  checks: read
+  contents: read
+  deployments: read
+  issues: read
+  packages: read
+  pull-requests: write
+  statuses: read
 
 jobs:
   reviewers: