Fix for MDEV-18276, typo in error message + all other occurrences of refering

mysql-test/include/mix2.inc

@@ -1153,7 +1153,7 @@ checksum table t1, t2, t3, t4, t5, t6, t7 extended;
 drop table t1,t2,t3, t4, t5, t6;
 
 #
-# Test problem with refering to different fields in same table in UNION
+# Test problem with referring to different fields in same table in UNION
 # (Bug#2552: UNION returns NULL instead of expected value (innoDB only tables))
 #
 eval create table t1 (id int,  name char(10) not null,  name2 char(10) not null) engine=$engine_type;

mysql-test/suite/innodb/t/innodb.test

@@ -1125,7 +1125,7 @@ checksum table t1, t2, t3, t4 extended;
 drop table t1,t2,t3;
 
 #
-# Test problem with refering to different fields in same table in UNION
+# Test problem with referring to different fields in same table in UNION
 # (Bug #2552)
 #
 create table t1 (id int,  name char(10) not null,  name2 char(10) not null) engine=innodb;

mysql-test/t/insert.test

 #
-# Test of refering to old values
+# Test of referring to old values
 #
 
 --disable_warnings