Select 通过menuTpl实现多行option，option被遮挡

#### 描述问题：

Select 通过menuTpl实现多行option，option被遮挡

#### 截图或视频：

#### 如何复现（请务必完整填写下面内容）：

1. 你是如何使用 amis 的？
在线demo
https://aisuda.github.io/amis-editor-demo

2. amis 版本是什么？请先在最新 beta 版本测试问题是否存在

3. 粘贴有问题的完整 `amis schema` 代码：
```
{
"type": "page",
"title": "Hello world",
"body": [
{
"type": "select",
"label": "选项",
"name": "select",
"options": [
{
"label": "选项A",
"value": "A"
},
{
"label": "选项B",
"value": "B"
}
],
"id": "u:cb2cea91e0ce",
"multiple": false,
"menuTpl": "

",
"itemHeight": 70
}
],
"id": "u:09f1354c1f96",
"asideResizor": false,
"pullRefresh": {
"disabled": true
}
}
```

4. 操作步骤
请简单描述一下复现的操作步骤...

Start with the supplied amis schema in the online demo, focusing on the Select configuration using menuTpl with multi-line options and itemHeight: 70. Reproduce the obstruction and inspect how the rendered option height and menu template interact. Done means each option's content is fully visible without being covered.

Written by the indexing model from the issue text.