MDEV-13626: Make test more robust

In commit b1742a5 we forgot
FLUSH TABLES, potentially causing errors for MyISAM system tables.

Author: dr-m

mysql-test/suite/innodb/t/xa_recovery_debug.test

@@ -4,6 +4,10 @@
 # Embedded server does not support restarting
 --source include/not_embedded.inc
 
+--disable_query_log
+FLUSH TABLES;
+--enable_query_log
+
 --echo #
 --echo # Bug#20872655 XA ROLLBACK IS NOT CRASH-SAFE
 --echo #