MDEV-26925 add test that there are no triggers in sys schema.

mysql-test/suite/sysschema/r/t_sys_config.result

+SELECT COUNT(*) FROM INFORMATION_SCHEMA.TRIGGERS WHERE TRIGGER_SCHEMA='sys';
+COUNT(*)
+0
 DESC sys.sys_config;
 Field	Type	Null	Key	Default	Extra
 variable	varchar(128)	NO	PRI	NULL	

mysql-test/suite/sysschema/t/t_sys_config.test

 -- source include/not_embedded.inc
 # Tests for sys schema
 # Verify the sys.sys_config table is as expected
-
+SELECT COUNT(*) FROM INFORMATION_SCHEMA.TRIGGERS WHERE TRIGGER_SCHEMA='sys';
 DESC sys.sys_config;
 
 SELECT variable, value, set_by FROM sys.sys_config ORDER BY 1;
@@ -11,7 +11,6 @@ UPDATE sys.sys_config SET value = 128 WHERE variable = 'statement_truncate_len';
 
 SELECT variable, value, set_by FROM sys.sys_config ORDER BY 1;
 
-# Ensure the sys.sys_config_insert_set_user trigger functions correctly
 INSERT INTO sys.sys_config (variable, value) VALUES ('foo', 'bar');
 
 SELECT variable, value, set_by FROM sys.sys_config ORDER BY 1;