Replace void with expect().toBeDefined() for getter side-effect access (S3735)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/stores/conformance.test.js

@@ -204,7 +204,7 @@ describe("conformanceStore", () => {
           attributes: [],
         },
       ];
-      void store.cases;
+      expect(store.cases).toBeDefined();
       // Original state should still contain the ISO date
       expect(store.allCases[0].started_at).toBe(originalDate);
     });