tests: byteify an `error.Abort` message in test-wireproto.py

Caught by PyCharm.

tests/test-wireproto.py

@@ -66,7 +66,7 class clientpeer(wireprotov1peer.wirepee
         elif isinstance(res, bytes):
             return res
         else:
-            raise error.Abort('dummy client does not support response type')
+            raise error.Abort(b'dummy client does not support response type')
 
     def _callstream(self, cmd, **args):
         return stringio(self._call(cmd, **args))