Incorrect user post count when guest account is not linked

[nielslange]

Steps to reproduce

1. Create a guest author account (guest-780)
2. Check post count for admin and guest author
3. Create one post (test-post-780) as guest author and remove admin as co-author
4. Check post count for admin and guest author

Note

The created post will increase the post count of the user that published the post on behalf of the guest author.

Expected behaviour

✅ Admin: 0 posts ✅ Guest: 1 post

Current behaviour

❌ Admin: 1 post ✅ Guest: 1 post

Related issue

#776