MDEV-24169 : Galera test failure on galera_rsu_simple

Add wait_condition.

mysql-test/suite/galera/t/galera_rsu_simple.test

@@ -8,6 +8,9 @@
 CREATE TABLE t1 (f1 INTEGER PRIMARY KEY) Engine=InnoDB;
 
 --connection node_2
+--let $wait_condition = SELECT COUNT(*) = 1 FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = 't1'
+--source include/wait_condition.inc
+
 SET SESSION wsrep_OSU_method = "RSU";
 ALTER TABLE t1 ADD COLUMN f2 INTEGER;
 SELECT COUNT(*) = 2 FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 't1';