Tweak pre-3.8 iscoroutine stub

Author: florimondmanca

stdlib/asyncio/coroutines.pyi

@@ -1,7 +1,6 @@
 import sys
-import types
 from collections.abc import Coroutine
-from typing import Any
+from typing import Any, AwaitableGenerator
 from typing_extensions import TypeGuard
 
 if sys.version_info >= (3, 11):
@@ -24,4 +23,4 @@ if sys.version_info >= (3, 8):
     def iscoroutine(obj: object) -> TypeGuard[Coroutine[Any, Any, Any]]: ...
 
 else:
-    def iscoroutine(obj: object) -> TypeGuard[types.GeneratorType[Any, Any, Any] | Coroutine[Any, Any, Any]]: ...
+    def iscoroutine(obj: object) -> TypeGuard[AwaitableGenerator[Any, Any, Any, Any] | Coroutine[Any, Any, Any]]: ...