MDEV-11018: rpl.rpl_mariadb_slave_capability fails sporadically in buildbot

The test was missing a wait_for_binlog_checkpoint.inc, making it non-deterministic
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>

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

@@ -20,6 +20,7 @@ SET @@global.debug_dbug='+d,simulate_slave_capability_none';
 
 connection master;
 FLUSH LOGS;
+--source include/wait_for_binlog_checkpoint.inc
 CREATE TABLE t1 (a INT PRIMARY KEY);
 INSERT INTO t1 VALUES (0);
 sync_slave_with_master;