Stabilize output of new isolation test insert-conflict-do-update-4.

Stabilize output of new isolation test insert-conflict-do-update-4.

The test added by commit 4b760a181 assumed that a table's physical
row order would be predictable after an UPDATE.  But a non-heap table
AM might produce some other order.  Even with heap AM, the assumption
seems risky; compare a3fd53bab for instance.  Adding an ORDER BY is
cheap insurance and doesn't break any goal of the test.

Author: Pavel Borisov <pashkin.elfe@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CALT9ZEHcE6tpvumScYPO6pGk_ASjTjWojLkodHnk33dvRPHXVw@mail.gmail.com
Backpatch-through: 14