fix: correct export of check lists

Fixes #255

src/plugins/lists/LexicalListItemVisitor.ts

@@ -1,4 +1,4 @@
-import { $isListItemNode, $isListNode, ListItemNode } from '@lexical/list'
+import { $isListItemNode, $isListNode, ListItemNode, ListNode } from '@lexical/list'
 import * as Mdast from 'mdast'
 import { LexicalExportVisitor } from '../../exportMarkdownFromLexical'
 
@@ -13,10 +13,11 @@ export const LexicalListItemVisitor: LexicalExportVisitor<ListItemNode, Mdast.Li
       const prevListItemNode = mdastParent.children.at(-1) as Mdast.ListItem
       actions.visitChildren(lexicalNode, prevListItemNode)
     } else {
+      const parentList = lexicalNode.getParent() as ListNode
       // nest the children in a paragraph for MDAST compatibility
       const listItem = actions.appendToParent(mdastParent, {
         type: 'listItem' as const,
-        checked: lexicalNode.getChecked(),
+        checked: parentList.getListType() === 'check' ? Boolean(lexicalNode.getChecked()) : undefined,
         spread: false,
         children: [{ type: 'paragraph' as const, children: [] }]
       }) as Mdast.ListItem