MessageBox: add missing type (#12118)

types/message-box.d.ts

@@ -126,6 +126,9 @@ export interface ElMessageBoxOptions {
 
   /** Error message when validation fails */
   inputErrorMessage?: string
+
+  /** Whether to distinguish canceling and closing */
+  distinguishCancelAndClose?: boolean
 }
 
 export interface ElMessageBoxShortcutMethod {