MDEV-26502 : galera.galera_applier_ftwrl_table_alter MTR failed : Result content mismatch

Add wait conditions and remove unnecessary sleep.

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

@@ -19,12 +19,17 @@ CREATE TABLE t1 (f1 INTEGER PRIMARY KEY) ENGINE=InnoDB;
 FLUSH TABLE t1 WITH READ LOCK;
 
 --connection node_2
+--let $wait_condition = SELECT COUNT(*) = 1 FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = 't1'
+--source include/wait_condition.inc
+
 ALTER TABLE t1 ADD COLUMN f2 INTEGER;
 
 --connection node_1
 SELECT 1 FROM DUAL;
-# Sleep for longer than the global timeout ...
---sleep 6
+# Wait
+--let $wait_condition = SELECT COUNT(*) = 1 FROM INFORMATION_SCHEMA.PROCESSLIST WHERE USER = 'system user' AND STATE = 'Waiting for table metadata lock';
+--source include/wait_condition.inc
+
 SELECT COUNT(*) = 1 FROM INFORMATION_SCHEMA.PROCESSLIST WHERE USER = 'system user' AND STATE = 'Waiting for table metadata lock';
 
 UNLOCK TABLES;