Merge branch 'dj-add-409-to-users-api' into 'master'

Add 409 Conflict return doc

See merge request gitlab-org/gitlab!75124

doc/api/users.md

@@ -1623,6 +1623,7 @@ Returns:
 - `201 Created` on success.
 - `404 User Not Found` if user cannot be found.
 - `403 Forbidden` if the user cannot be approved because they are blocked by an administrator or by LDAP synchronization.
+- `409 Conflict` if the user has been deactivated.
 
 Example Responses: