fix protobuf version

Wei Chu · Wei Chu · commit ef19cb7537e9 · 2022-08-10T10:52:05.000-07:00
diff --git a/tox.ini b/tox.ini
@@ -70,6 +70,7 @@ deps =
     six
     future
     pyyaml
+    protobuf <= 3.20.1  #https://exerror.com/typeerror-descriptors-cannot-not-be-created-directly/
 
 [testenv:flake8]
 basepython = python3
