Wait for next tick in subscription test

Replicates graphql/graphql-js@4f26a6b

Author: Cito

tests/subscription/test_subscribe.py

@@ -1,3 +1,5 @@
+import asyncio
+
 from typing import Any, Dict, Optional, Callable
 
 from pytest import mark, raises  # type: ignore
@@ -222,6 +224,7 @@ async def accepts_type_definition_with_async_subscribe_function():
         pubsub = EventEmitter()
 
         async def subscribe_email(_inbox, _info):
+            await asyncio.sleep(0)
             return EventEmitterAsyncIterator(pubsub, "importantEmail")
 
         schema = GraphQLSchema(