tenacity.retry(sleep=...) fails type-checking with async sleep function

[cjwatson]

Since tenacity 9.1.3, the following program (reduced from real code) fails to type-check:

import asyncio

import tenacity


async def _tenacity_sleep(delay: float) -> None:
    await asyncio.sleep(delay)


@tenacity.retry(sleep=_tenacity_sleep)
async def do_wait_for_messages() -> None:
    pass

$ mypy --strict t.py
t.py:10: error: Argument 1 has incompatible type "Callable[[], Coroutine[Any, Any, None]]"; expected "Callable[[], Awaitable[Never]]"  [arg-type]
Found 1 error in 1 file (checked 1 source file)

The corresponding sync variant still type-checks fine.

I assume this has something to do with the new return type annotation in the async overload variant introduced by #551, but I haven't quite been able to puzzle it out. Maybe @Zac-HD can help, since this was their change?

[Zac-HD]

Yep, I found this yesterday and have just been testing my patch very carefully to avoid a third round.