Doc: Fix incorrect reference to conflicting column in pg_replication_slots.
Commit
007693f2a3 changes the existing 'conflicting' field to
'conflict_reason' in pg_replication_slots but missed updating one of its
existing references.
Author: Hou Zhijie
Discussion: https://postgr.es/m/OS0PR01MB571690299199ACA80F602D97947E2@OS0PR01MB5716.jpnprd01.prod.outlook.com