update type hints

Author: maxfischer2781

asyncstdlib/itertools.pyi

@@ -16,13 +16,17 @@ from ._typing import AnyIterable, ADD, T, T1, T2, T3, T4, T5
 
 def cycle(iterable: AnyIterable[T]) -> AsyncIterator[T]: ...
 @overload
-def accumulate(iterable: AnyIterable[ADD]) -> AsyncIterator[ADD]: ...
+def accumulate(
+    iterable: AnyIterable[ADD], *, initial: None = ...
+) -> AsyncIterator[ADD]: ...
 @overload
 def accumulate(iterable: AnyIterable[ADD], *, initial: ADD) -> AsyncIterator[ADD]: ...
 @overload
 def accumulate(
     iterable: AnyIterable[T],
     function: Callable[[T, T], T] | Callable[[T, T], Awaitable[T]],
+    *,
+    initial: None = ...,
 ) -> AsyncIterator[T]: ...
 @overload
 def accumulate(