add a test for drop trigger under --read-only

mysql-test/r/read_only.result

@@ -6,6 +6,7 @@ connection default;
 set global read_only=0;
 connection con1;
 create table t1 (a int);
+create trigger trg1 before insert on t1 for each row set @a:=1;
 insert into t1 values(1);
 create table t2 select * from t1;
 connection default;
@@ -20,6 +21,8 @@ create table t3 (a int);
 ERROR HY000: The MariaDB server is running with the --read-only option so it cannot execute this statement
 insert into t1 values(1);
 ERROR HY000: The MariaDB server is running with the --read-only option so it cannot execute this statement
+drop trigger trg1;
+ERROR HY000: The MariaDB server is running with the --read-only option so it cannot execute this statement
 update t1 set a=1 where 1=0;
 ERROR HY000: The MariaDB server is running with the --read-only option so it cannot execute this statement
 update t1,t2 set t1.a=t2.a+1 where t1.a=t2.a;

mysql-test/t/read_only.test

@@ -30,6 +30,7 @@ set global read_only=0;
 connection con1;
 
 create table t1 (a int);
+create trigger trg1 before insert on t1 for each row set @a:=1;
 
 insert into t1 values(1);
 
@@ -56,6 +57,9 @@ create table t3 (a int);
 --error ER_OPTION_PREVENTS_STATEMENT
 insert into t1 values(1);
 
+--error ER_OPTION_PREVENTS_STATEMENT
+drop trigger trg1;
+
 # if a statement, after parse stage, looks like it will update a
 # non-temp table, it will be rejected, even if at execution it would
 # have turned out that 0 rows would be updated