MDEV-22949 perfschema.memory_aggregate_no_a_no_u fails sporadically in buildbot with wrong result

perfschema aggregation, like SHOW STATUS, is only statistically correct.
It doesn't use atomics for performance reasons and might miss individual
increments, particularly when two connections are disconnecting at the
same time.

To have stable results tests should avoid doing it.

mysql-test/suite/perfschema/include/memory_aggregate_load.inc

@@ -274,7 +274,6 @@ execute dump_users;
 execute dump_hosts;
 
 --disconnect con1
---disconnect con5
 
 --connection default
 
@@ -283,6 +282,8 @@ let $wait_condition=
   select count(*) = 0 from performance_schema.threads
   where `TYPE`='FOREGROUND' and PROCESSLIST_USER= 'user1';
 --source include/wait_condition.inc
+
+--disconnect con5
 let $wait_condition=
   select count(*) = 1 from performance_schema.threads
   where `TYPE`='FOREGROUND' and PROCESSLIST_USER= 'user4';