test: improve test case

Author: edison1105

packages/runtime-core/__tests__/apiWatch.spec.ts

@@ -1138,6 +1138,8 @@ describe('api: watch', () => {
     const root = nodeOps.createElement('div')
     createApp(Comp).mount(root)
     expect(instance!.scope.effects.length).toBe(3)
+    
     instance!.scope.stop()
+    expect(instance!.scope.effects[0].active).toBe(false)
   })
 })