MDEV-16708: fixed issue with handling of the directive --enable-prepared-warnings in mysqltest

mysql-test/main/trigger.test

@@ -761,6 +761,7 @@ drop table t1;
 
 create table t1 (id int, data int, username varchar(16));
 insert into t1 (id, data) values (1, 0);
+--enable_prepare_warnings
 delimiter |;
 create trigger t1_whoupdated before update on t1 for each row
 begin
@@ -771,6 +772,7 @@ begin
   select count(*) from ((select 1) union (select 2)) as d1 into i;
 end|
 delimiter ;|
+--disable_prepare_warnings
 update t1 set data = 1;
 
 connection addconroot1;
@@ -2343,6 +2345,7 @@ DROP TABLE IF EXISTS t1, t2;
 CREATE TABLE t1 (b VARCHAR(50) NOT NULL);
 CREATE TABLE t2 (a VARCHAR(10) NOT NULL DEFAULT '');
 
+--enable_prepare_warnings
 delimiter //;
 CREATE TRIGGER trg1 AFTER INSERT ON t2
 FOR EACH ROW BEGIN
@@ -2350,6 +2353,7 @@ FOR EACH ROW BEGIN
     (@bug51650 IS NULL OR @bug51650 != c.b) AND c.b = NEW.a LIMIT 1 INTO @foo;
 END//
 delimiter ;//
+--disable_prepare_warnings
 
 SET @bug51650 = 1;
 INSERT IGNORE INTO t2 VALUES();