allow invalid response_types for GetChallengeResponses

I havent dug into the purpose of response_types yet, but this package short circuits when a response type is given that it does not expect. We have an open issue with the package here serverstf#83. For now, this unblocks us with rocksteady

valve/source/messages.py

@@ -473,7 +473,7 @@ class InfoResponse(Message):
 class GetChallengeResponse(Message):
 
     fields = (
-        ByteField("response_type", validators=[lambda x: x == 0x41]),
+        ByteField("response_type", validators=[lambda x: x == 0x41 or x == 69]),
         LongField("challenge")
     )