rpcsrv: fix TestFilteredNotaryRequestSubscriptions

Add closing of the server, as it does in other subscription tests.

Close #3378

Signed-off-by: Ekaterina Pavlova <ekt@morphbits.io>

pkg/services/rpcsrv/subscription_test.go

@@ -391,6 +391,7 @@ func TestFilteredNotaryRequestSubscriptions(t *testing.T) {
 
 	chain, rpcSrv, c, respMsgs, finishedFlag := initCleanServerAndWSClient(t)
 	rpcSrv.coreServer.Start()
+	defer rpcSrv.coreServer.Shutdown()
 
 	// blocks are needed to make GAS deposit for priv0
 	blocks := getTestBlocks(t)