MessageBox: fix type definition (#14278)
MessageBox: fix type definition (#14278)

`MessageBoxData` may be a action string
https://github.com/ElemeFE/element/blob/b2f0958089a197907afdbea450a9faec69b48f02/packages/message-box/src/main.js#L57-L62
ElemeFE/element,ElemeFE/element