Fixed multi_update_debug.test

Backported fix from 10.5

mysql-test/r/multi_update_debug.result

@@ -5,9 +5,10 @@ insert t2 values (5,6),(7,8);
 create table t0 (x int);
 insert t0 values (11), (22);
 create trigger tr1 before update on t1 for each row insert t0 values (new.b);
-set debug_sync='open_tables_after_open_and_process_table WAIT_FOR cont';
+set debug_sync='open_tables_after_open_and_process_table SIGNAL ready WAIT_FOR cont';
 update t1 join t2 on (a=c+4) set b=d;
 connect con1, localhost, root;
+set debug_sync='now WAIT_FOR ready';
 set debug_sync='mdl_acquire_lock_wait SIGNAL cont';
 lock table t1 write, t0 write;
 disconnect con1;

mysql-test/t/multi_update_debug.test

@@ -10,12 +10,11 @@ create table t0 (x int);
 insert t0 values (11), (22);
 create trigger tr1 before update on t1 for each row insert t0 values (new.b);
 
-set debug_sync='open_tables_after_open_and_process_table WAIT_FOR cont';
+set debug_sync='open_tables_after_open_and_process_table SIGNAL ready WAIT_FOR cont';
 send update t1 join t2 on (a=c+4) set b=d;
 
 connect con1, localhost, root;
-let $wait_condition= select count(*) from information_schema.processlist where state = ' debug sync point: open_tables_after_open_and_process_table'
-source include/wait_condition.inc;
+set debug_sync='now WAIT_FOR ready';
 set debug_sync='mdl_acquire_lock_wait SIGNAL cont';
 lock table t1 write, t0 write;
 let $wait_condition= select count(*) from information_schema.processlist where state = 'Waiting for table metadata lock'