Make pylint happy

It complains about unreachable code - it is an assert about this line
being unreachable (if it is reached, it means there is a bug somewhere).
Since it's critical that this function do not return in the case of
invalid response, keep the assert.

qrexec/tools/qrexec_policy_exec.py

@@ -114,6 +114,7 @@ async def execute(self) -> str:
             ask_response,
         )
         self.handle_invalid_response()
+        # pylint: disable=unreachable
         assert False, "handle_invalid_response should throw"