chore: mark the unmanaged dependency check required (#3517)

b/326247198

Author: suztomo

Diff for: .github/sync-repo-settings.yaml

@@ -21,6 +21,7 @@ branchProtectionRules:
       - compile (11)
       - units-with-multiplexed-session (8)
       - units-with-multiplexed-session (11)
+      - unmanaged_dependency_check
   - pattern: 3.3.x
     isAdminEnforced: true
     requiredApprovingReviewCount: 1