disable a test on MySQL

MySQL cast() doesn't do truncation, this never worked properly

Signed-off-by: Gavin King <gavin@hibernate.org>

hibernate-core/src/test/java/org/hibernate/orm/test/query/hql/FunctionTests.java

@@ -1131,6 +1131,7 @@ public class FunctionTests {
 
 	@Test
 	@SkipForDialect( dialectClass = AltibaseDialect.class, reason = "Altibase cast to char does not do truncatation")
+	@SkipForDialect( dialectClass = MySQLDialect.class, matchSubTypes = true, reason = "MySQL cast does not do truncatation")
 	public void testCastFunctionWithLength(SessionFactoryScope scope) {
 		scope.inTransaction(
 				session -> {