MDEV-7157 plugins.server_audit fails sporadically in buildbot.

  Records can get to the different place in the log when multiple thread
    are logged. So the delay added to let the record be saved on the same
    place.

mysql-test/suite/plugins/t/server_audit.test

@@ -43,6 +43,7 @@ show variables like 'server_audit%';
 set global server_audit_mode=1;
 set global server_audit_events='';
 create database sa_db;
+--sleep 2
 connect (con1,localhost,root,,test);
 connection con1;
 create table t1 (id2 int);