Move async channel to tests (#36)

Author: AdrienVannson

src/betterproto2/grpc/util/__init__.py

@@ -8,7 +8,7 @@
 import pytest
 from grpclib.testing import ChannelFor
 
-from betterproto2.grpc.util.async_channel import AsyncChannel
+from tests.grpc.async_channel import AsyncChannel
 from tests.output_betterproto.service import (
     DoThingRequest,
     DoThingResponse,

src/betterproto2/grpc/util/async_channel.py renamed to tests/grpc/async_channel.py

@@ -5,7 +5,7 @@
 import pytest
 
 import betterproto2
-from betterproto2.grpc.util.async_channel import AsyncChannel
+from tests.grpc.async_channel import AsyncChannel
 
 
 @dataclass