fix: shallowReadonly should work for ref

Author: ygj6

test/v3/reactivity/readonly.spec.ts

@@ -399,9 +399,7 @@ describe('reactivity/readonly', () => {
         },
       }).$mount()
 
-      expect(vm.$el.textContent).toBe(`{
-  "number": 0
-} 0`)
+      expect(vm.$el.textContent).toBe(`{\n  "number": 0\n} 0`)
     })
   })
 })