docs(mentions): fix notFoundContent props type definition (#5461)

Author: buqiyuan

components/mentions/index.en-US.md

@@ -21,7 +21,7 @@ When you need to mention someone or something.
 | defaultValue | Default value | string |  |
 | filterOption | Customize filter option logic | false \| (input: string, option: OptionProps) => boolean |  |
 | getPopupContainer | Set the mount HTML node for suggestions | () => HTMLElement |  |
-| notFoundContent | Set mentions content when not match | ReactNode | 'Not Found' |
+| notFoundContent | Set mentions content when not match | string \| slot | 'Not Found' |
 | placement | Set popup placement | `top` \| `bottom` | `bottom` |
 | prefix | Set trigger prefix keyword | string \| string\[] | '@' |
 | split | Set split string before and after selected mention | string | ' ' |

components/mentions/index.zh-CN.md

@@ -22,7 +22,7 @@ cover: https://gw.alipayobjects.com/zos/alicdn/jPE-itMFM/Mentions.svg
 | defaultValue | 默认值 | string |  |
 | filterOption | 自定义过滤逻辑 | false \| (input: string, option: OptionProps) => boolean |  |
 | getPopupContainer | 指定建议框挂载的 HTML 节点 | () => HTMLElement |  |
-| notFoundContent | 当下拉列表为空时显示的内容 | ReactNode | 'Not Found' |
+| notFoundContent | 当下拉列表为空时显示的内容 | string \| slot | 'Not Found' |
 | placement | 弹出层展示位置 | `top` \| `bottom` | `bottom` |
 | prefix | 设置触发关键字 | string \| string\[] | '@' |
 | split | 设置选中项前后分隔符 | string | ' ' |