MDEV-7187 perfschema.aggregate fails sporadically in buildbot

During slow execution, e.g. under valgrind, there was a chance
that Aria checkpoint would happen while P_S tables were being
queried; it could cause different data in joined P_S, and
thus combinations of results that the test did not expect.

Fixed by disabling Aria checkpoints for the test.

mysql-test/suite/perfschema/r/aggregate.result

 "General cleanup"
+set @aria_checkpoint_interval_save= @@global.aria_checkpoint_interval;
+set @@global.aria_checkpoint_interval= 0;
 drop table if exists t1;
 update performance_schema.setup_instruments set enabled = 'NO';
 update performance_schema.setup_consumers set enabled = 'NO';
@@ -116,3 +118,4 @@ update performance_schema.setup_consumers set enabled = 'YES';
 update performance_schema.setup_instruments
 set enabled = 'YES', timed = 'YES';
 drop table test.t1;
+set @@global.aria_checkpoint_interval= @aria_checkpoint_interval_save;

mysql-test/suite/perfschema/t/aggregate.test

@@ -6,6 +6,10 @@
 
 --echo "General cleanup"
 
+# MDEV-7187 - test fails sporadically in buildbot
+set @aria_checkpoint_interval_save= @@global.aria_checkpoint_interval;
+set @@global.aria_checkpoint_interval= 0;
+
 --disable_warnings
 drop table if exists t1;
 --enable_warnings
@@ -188,3 +192,6 @@ update performance_schema.setup_instruments
   set enabled = 'YES', timed = 'YES';
 
 drop table test.t1;
+
+set @@global.aria_checkpoint_interval= @aria_checkpoint_interval_save;
+