Since commit f0f13a3a, we estimate
ModifyTable paths without a RETURNING clause differently.  Update an
example from the manual that showed the old behavior.

Author: Takayuki Tsunakawa <tsunakawa.takay@fujitsu.com>
Reviewed-by: Laurenz Albe <laurenz.albe@cybertec.at>
Discussion: https://postgr.es/m/TYAPR01MB29905674F41693BBA9DA28CAFEA20%40TYAPR01MB2990.jpnprd01.prod.outlook.com