BUG#41653 rpl_innodb_bug30888 fails sporadically on pushbuild: warning in log

In mtr.check_warnings, `text` was declares as type text, which is
64K, and when the server log grows larger than this, it would be
truncated, and then check_warnings was actually checking the 
error messages of a previous test and complain warnings.

This patch fixed the problem by change the type of `text` to
mediumtext, which is 16M.

mysql-test/include/mtr_warnings.sql

@@ -219,7 +219,7 @@ INSERT INTO global_suppressions VALUES
 --
 CREATE DEFINER=root@localhost PROCEDURE check_warnings(OUT result INT)
 BEGIN
-  DECLARE `text` text charset utf8;
+  DECLARE `text` mediumtext charset utf8;
   DECLARE `pos` bigint unsigned;
 
   -- Don't write these queries to binlog