Base transports w/ 'operations_client' have incorrect typing #1028
Description
From mypy:
google/cloud/datastore_admin_v1/services/datastore_admin/transports/grpc_asyncio.py:297: error: Return type "OperationsAsyncClient" of "operations_client" incompatible with return type "OperationsClient" in supertype "DatastoreAdminTransport"
The sync / async operations client types share no common base class (beyond object). The base transport shouldn't declare any typing at all.