MDEV-20528 innodb.purge_secondary_mdev-16222 failed in buildbot, debug sync point wait timed out

mysql-test/suite/gcol/t/innodb_virtual_debug_purge.test

@@ -264,8 +264,9 @@ DROP TABLE t1, t2;
 --echo # on table with virtual columns and indexes
 --echo #
 
+--source suite/innodb/include/wait_all_purged.inc
 --let $datadir= `select @@datadir`
-SET @saved_dbug= @@GLOBAL.debug_dbug;
+set @saved_dbug= @@global.debug_dbug;
 set global debug_dbug= "+d,ib_purge_virtual_mdev_16222_1,ib_purge_virtual_mdev_16222_2";
 
 create table t1 (
@@ -373,4 +374,4 @@ SELECT * FROM t1;
 # Cleanup
 DROP TABLE t1;
 SET debug_sync= reset;
-set global debug_dbug= @saved_dbug;
\ No newline at end of file
+set global debug_dbug= @saved_dbug;