crud导出excel，导出选定行不生效

[ylturbo]

描述问题：

crud组件导出excel，在勾选需要导出的行之后，导出的excel为空

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？
   sdk

2. amis 版本是什么？请先在最新 beta 版本测试问题是否存在
   版本6.11.0，官网上的示例

3. 粘贴有问题的完整 amis schema 代码：

{
  "type": "page",
  "body": {
    "type": "crud",
    "syncLocation": false,
    "api": "/amis/api/mock2/sample",
    "headerToolbar": [
      "bulkActions",
      {
        "type": "export-excel",
        "label": "${selectedIndexes|join}",
        "rowSlice": "${selectedIndexes|join}"
      }
    ],
    "bulkActions": [
      {
        "label": "批量删除",
        "actionType": "ajax",
        "api": "delete:/amis/api/mock2/sample/${ids|raw}",
        "confirmText": "确定要批量删除?"
      },
      {
        "label": "批量修改",
        "actionType": "dialog",
        "dialog": {
          "title": "批量编辑",
          "body": {
            "type": "form",
            "api": "/amis/api/mock2/sample/bulkUpdate2",
            "body": [
              {
                "type": "hidden",
                "name": "ids"
              },
              {
                "type": "input-text",
                "name": "engine",
                "label": "Engine"
              }
            ]
          }
        }
      }
    ],
    "columns": [
      {
        "name": "id",
        "label": "ID"
      },
      {
        "name": "engine",
        "label": "Rendering engine"
      },
      {
        "name": "browser",
        "label": "Browser"
      },
      {
        "name": "platform",
        "label": "Platform(s)"
      },
      {
        "name": "version",
        "label": "Engine version"
      },
      {
        "name": "grade",
        "label": "CSS grade"
      }
    ]
  }
}

4. 操作步骤