Make AsyncGeneratorType.aclose() properly return Awaitable[None]

[elradu]

It seems changing for AsyncGeneratorType as well was omitted when closing #2785

Signed-off-by: Radu Matei Lacraru rml97@fb.com

[elradu]

from typing import AsyncGenerator


async def a() -> AsyncGenerator[int, None]:
    yield 1


reveal_type(a().aclose)

mypy example.py yields:

example.py:8: error: Revealed type is 'def () -> typing.Awaitable[builtins.int*]'

mypy --custom-typeshed ~/typeshed example.py yields:

example.py:8: error: Revealed type is 'def () -> typing.Awaitable[None]'

[srittau]

Thanks!