Suppress warning on galera_ssl_upgrade test.

mysql-test/suite/galera/r/galera_ssl_upgrade.result

@@ -5,6 +5,10 @@ SELECT VARIABLE_VALUE = 2 FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_N
 VARIABLE_VALUE = 2
 1
 connection node_1;
+call mtr.add_suppression("WSREP: write_handler(): protocol is shutdown.*");
+connection node_2;
+call mtr.add_suppression("WSREP: write_handler(): protocol is shutdown.*");
+connection node_1;
 connection node_2;
 connection node_1;
 SELECT VARIABLE_VALUE = 2 FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_NAME = 'wsrep_cluster_size';

mysql-test/suite/galera/t/galera_ssl_upgrade.test

@@ -11,6 +11,11 @@
 SELECT VARIABLE_VALUE = 'Synced' FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_NAME = 'wsrep_local_state_comment';
 SELECT VARIABLE_VALUE = 2 FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_NAME = 'wsrep_cluster_size';
 
+--connection node_1
+call mtr.add_suppression("WSREP: write_handler(): protocol is shutdown.*");
+--connection node_2
+call mtr.add_suppression("WSREP: write_handler(): protocol is shutdown.*");
+
 # Setup galera ports
 --connection node_1
 --source suite/galera/include/galera_base_port.inc