docs: v3 -> v4 deprecate Button.Group (#26260)

* docs: v3 -> v4 deprecate Button.Group

* docs: update

docs/react/migration-v4.en-US.md

@@ -56,6 +56,7 @@ This document will help you upgrade from antd `3.x` version to antd `4.x` versio
 - Removed the `lazy` attribute of Transfer, which did not really optimize the effect.
 - Removed `combobox` mode, please use `AutoComplete` instead.
 - Removed the `rowSelection.hideDefaultSelections` property of Table, please use `SELECTION_ALL` and `SELECTION_INVERT` in `rowSelection.selections` instead, [Custom Selection](/components/table/#components-table-demo-row-selection-custom).
+- Deprecated Button.Group, please use `Space` instead.
 
 #### Icon upgrade
 

docs/react/migration-v4.zh-CN.md

@@ -56,6 +56,7 @@ title: 从 v3 到 v4
 - 移除了 Transfer 的 `lazy` 属性，它并没有起到真正的优化效果。
 - 移除了 Select 的 `combobox` 模式，请使用 `AutoComplete` 替代。
 - 移除了 Table 的 `rowSelection.hideDefaultSelections` 属性，请在 `rowSelection.selections` 中使用 `SELECTION_ALL` 和 `SELECTION_INVERT` 替代，[自定义选择项](/components/table/#components-table-demo-row-selection-custom)。
+- 废弃 Button.Group，请使用 `Space` 代替。
 
 #### 图标升级