The discouragement threshold is modified to account for the change in D6036, which caused a peer to be banned after only 10 out-of-order messages instead of 100.
Using the wrong value in this test could potentially cause the node to be banned before all messages are sent, and cause the next self.send_message(msg_verack()) to break the test, because this method fails when trying to send a message if the connection is closed.
I observed this failure while trying core#19657 (D10063), in which the message is sent a bit later in the test and the node bans the p2p connection faster.