[0.5.0] Minor issue: async only client generated proto includes non-existent classes

[FrankC01]

Generated using
protoc -I./sui/ -I./sui/sui/rpc/v2beta/ --python_betterproto2_opt=typing.310 --python_betterproto2_opt=client_generation=async --python_betterproto2_out=src/suimsg ./sui/sui/rpc/v2beta/*.proto

__init__.py in the __all__ declaration adds a '<ServiceNameBase' for each Stub

    "LedgerServiceStub",
    "LedgerServiceBase",
    "TransactionExecutionServiceStub",
    "TransactionExecutionServiceBase",

[AdrienVannson]

Fixed by betterproto/python-betterproto2-compiler#77