MDEV-15393: Fix rpl_mysqldump_gtid_slave_pos

The slave would try to sync_with_master_gtid.inc,
but the master never actually saved its gtid position
so the test would move on too quickly.

mysql-test/suite/rpl/r/rpl_mysqldump_gtid_slave_pos.result

@@ -30,6 +30,7 @@ insert into t1 set a = 4;
 insert into t1 set a = 3;
 insert into t1 set a = 2;
 insert into t1 set a = 1;
+include/save_master_gtid.inc
 connection slave;
 include/start_slave.inc
 include/sync_with_master_gtid.inc

mysql-test/suite/rpl/t/rpl_mysqldump_gtid_slave_pos.test

@@ -44,6 +44,7 @@ while ($i)
   eval insert into t1 set a = $i;
   --dec $i
 }
+--source include/save_master_gtid.inc
 
 --connection slave
 --source include/start_slave.inc