Add a note why we're expecting two messages

As the adversary has turned of signature verification, we should expect
to see two messages (the correctly signed and the incorrectly signed
one) when we publish. Those that have verification on, should only see
one.

floodsub_test.go

@@ -1022,6 +1022,9 @@ func TestImproperlySignedMessageRejected(t *testing.T) {
 	<-time.After(1 * time.Second)
 	adversaryCancel()
 
+	// Ensure the adversary successfully publishes the incorrectly signed
+	// message. If the adversary "sees" this, we successfully got through
+	// their local validation.
 	if len(adversaryMessages) != 2 {
 		t.Fatalf("got %d messages, expected 2", len(adversaryMessages))
 	}