Fix useLoadableQuery tests affected by variables change

src/react/hooks/__tests__/useLoadableQuery.test.tsx

@@ -5099,7 +5099,7 @@ it("can subscribe to subscriptions and react to cache updates via `subscribeToMo
       subscriptionData: {
         data: { greetingUpdated: "Subscription hello" },
       },
-      variables: {},
+      variables: undefined,
     }
   );
 });