Fix optimistic ack test and note randomness dependency

quic/s2n-quic/src/tests/skip_packets.rs

@@ -88,8 +88,11 @@ fn optimistic_ack_mitigation() {
 
     // Verify that both client and server are skipping packets for Optimistic
     // Ack attack mitigation.
-    assert_eq!(server_skip_count, 5);
-    assert_eq!(client_skip_count, 5);
+    //
+    // The exact number of skipped packets depends on randomness, so this test may be changed by
+    // unrelated changes. The important thing is that both numbers are non-zero.
+    assert_eq!(server_skip_count, 4);
+    assert_eq!(client_skip_count, 4);
 }
 
 // Mimic an Optimistic Ack attack and confirm the connection is closed with