Update to the latest version of grpcio-tools

[parthea]

PR #87 regenerated pb2 files using the latest version of grpcio-tools. There is an issue reported in #91 where the changes result in AttributeError: 'NoneType' object has no attribute 'message_types_by_name'. I was able to reproduce the issue in a virtual environment using the steps in #91. The issue is no longer present when I pin grpcio-tools<1.44.0 and regenerate protos using the previous version of grpcio-tools.

I've opened #93 to pin the version of grpcio-tools so development can continue in this repo.

[lidizheng]

A similar issue is reported at protocolbuffers/protobuf#8803.

[lidizheng]

Can you try to bump the version of ProtoBuf and try again? For each gRPC release, we will try to use the ProtoBuf latest release at given time.

[parthea]

Thanks @lidizheng ! We'll bump the minimum protobuf to 3.15.0 here https://github.com/googleapis/python-api-common-protos/blob/main/setup.py#L25 .

Version 3.15.0 doesn't have the error. In addition, the issue reported in #91 was using a pre-release version protobuf 4.0.0rc2 which is yanked. I tested the latest pre-release for protobuf version protobuf-3.20.0rc2 and couldn't reproduce the issue.