fix: attachment policy editing modal crashes when opened (#3663)

#### What type of PR is this?

/kind bug
/area console
/milestone 2.5.x

#### What this PR does / why we need it:

修复附件存储策略编辑表单无法正常渲染的问题。此问题原因为 Modal 组件使用了 OverlayScrollbars 库来模拟滚动条，但在初始化的时候由于 Body 没有任何子元素，所以导致异常。

#### Which issue(s) this PR fixes:

Fixes #3662 

#### Special notes for your reviewer:

测试是否能够正常打开附件存储策略编辑表单即可。

#### Does this PR introduce a user-facing change?

```release-note
修复 Console 端附件存储策略编辑表单无法正常渲染的问题
```

console/src/modules/contents/attachments/components/AttachmentPolicyEditingModal.vue

@@ -207,6 +207,7 @@ const onVisibleChange = (visible: boolean) => {
     :width="600"
     @update:visible="onVisibleChange"
   >
+    <div>
       <FormKit
         v-if="formSchema && configMapFormData"
         id="attachment-policy-form"
@@ -233,6 +234,7 @@ const onVisibleChange = (visible: boolean) => {
           :data="configMapFormData['default']"
         />
       </FormKit>
+    </div>
 
     <template #footer>
       <VSpace>