fix(接口测试): 修复断言响应时间开启关闭不生效的缺陷

--bug=1026919 --user=王孝刚 【接口测试】新建场景-添加场景断言-响应时间-点击关闭开关仍显示开启状态
https://www.tapd.cn/55049933/s/1380894

api-test/frontend/src/business/definition/components/assertion/ApiAssertionDuration.vue

@@ -59,7 +59,7 @@ export default {
     add() {
       if (this.validate()) {
         this.duration.value = this.value;
-        this.duration.enable = true;
+        this.$set(this.duration, 'enable', true);
         this.callback();
       }
     },