test_slot_timelines: Fix alternate expected output

src/test/modules/test_slot_timelines/expected/load_extension_1.out

 CREATE EXTENSION test_slot_timelines;
 SELECT test_slot_timelines_create_logical_slot('test_slot', 'test_decoding');
 ERROR:  replication slots can only be used if max_replication_slots > 0
-SELECT test_slot_timelines_advance_logical_slot('test_slot', txid_current(), txid_current(), pg_current_xlog_location(), pg_current_xlog_location());
+SELECT test_slot_timelines_advance_logical_slot('test_slot', txid_current()::text::xid, txid_current()::text::xid, pg_current_xlog_location(), pg_current_xlog_location());
 ERROR:  replication slots can only be used if max_replication_slots > 0
 SELECT pg_drop_replication_slot('test_slot');
 ERROR:  replication slots can only be used if max_replication_slots > 0