correct codes of warnings in result file

mysql-test/r/func_gconcat.result

@@ -150,10 +150,10 @@ grp	group_concat(c)
 4	
 5	NULL
 Warnings:
-Warning	1254	1 line(s) was(were) cut by group_concat()
+Warning	1258	1 line(s) was(were) cut by group_concat()
 show warnings;
 Level	Code	Message
-Warning	1254	1 line(s) was(were) cut by group_concat()
+Warning	1258	1 line(s) was(were) cut by group_concat()
 select group_concat(sum(a)) from t1 group by grp;
 Invalid use of group function
 select grp,group_concat(c order by 2) from t1 group by grp;