Fix a random failure in 003_logical_slots.pl.

Fix a random failure in 003_logical_slots.pl.

The failed test was trying to validate that the two_phase option for a
slot is retained after the upgrade. The problem was that it didn't get
enabled before the upgrade so expecting to be enabled after the upgrade
was not right in the first place. This is a timing issue because we enable
the two_phase once the initial sync for all the tables is finished.
Normally, we wait for the two_phase state to be enabled but this test
missed that step.

Per buildfarm.

Author: Hayato Kuroda
Discussion: https://postgr.es/m/TY3PR01MB98892396D1071FC4320D6B31F586A@TY3PR01MB9889.jpnprd01.prod.outlook.com