Fix LSN format in debug message

Commit 2633dae2e4 standardized all existing messages to use `%X/%08X`
for LSNs, but this one crept back in after the commit.

src/backend/replication/logical/worker.c

@@ -4587,7 +4587,7 @@ wait_for_local_flush(RetainDeadTuplesData *rdt_data)
 	MyLogicalRepWorker->oldest_nonremovable_xid = rdt_data->candidate_xid;
 	SpinLockRelease(&MyLogicalRepWorker->relmutex);
 
-	elog(DEBUG2, "confirmed flush up to remote lsn %X/%X: new oldest_nonremovable_xid %u",
+	elog(DEBUG2, "confirmed flush up to remote lsn %X/%08X: new oldest_nonremovable_xid %u",
 		 LSN_FORMAT_ARGS(rdt_data->remote_lsn),
 		 rdt_data->candidate_xid);