[tutorial] Reactions update is broken in `<SinglePostPage />`

Steps To Reproduce

1. Click "View Post" for any post
2. Click the reactions

Link to code example: The codesandbox here

The current behavior

Reactions work for the post list page, not for the single post page.

The expected behavior

1. Reactions work for single post page
2. Reactions sync in both list list page and single post page.