fix typo (#6106)

Author: ryo-manba

packages/@react-stately/data/docs/useListData.mdx

@@ -94,10 +94,10 @@ list.insert(1, {name: 'Horse'}, {name: 'Giraffe'});
 
 ```tsx
 // Insert an item before another item
-list.insertAfter('Kangaroo', {name: 'Horse'});
+list.insertBefore('Kangaroo', {name: 'Horse'});
 
 // Insert multiple items before another item
-list.insertAfter('Kangaroo', {name: 'Horse'}, {name: 'Giraffe'});
+list.insertBefore('Kangaroo', {name: 'Horse'}, {name: 'Giraffe'});
 ```
 
 ```tsx