Fix iscoroutinefunction check (for both inspect & asyncio)

[NatureGeorge]

#263 did not fully solve #224.

current behavior

python -m pip install git+https://github.com/jd/tenacity.git@be9bccbb731d28ab0bcd8a4ee5acae70988bf593

from inspect import iscoroutinefunction as inspect_iscoroutinefunction
from asyncio import iscoroutinefunction as asyncio_iscoroutinefunction

from tenacity import retry


async def a():
    pass

print(inspect_iscoroutinefunction(a), asyncio_iscoroutinefunction(a))

b = retry(a)

print(inspect_iscoroutinefunction(b), asyncio_iscoroutinefunction(b))

True True
False True

How to solve

tenacity/tenacity/_asyncio.py

Line 78 in be9bccb

fn._is_coroutine = asyncio.coroutines._is_coroutine

The reason that it passes asyncio.iscoroutinefunction is:

https://docs.python.org/3/library/asyncio-task.html#asyncio.iscoroutinefunction

asyncio.iscoroutinefunction(func)
Return True if func is a coroutine function.
This method is different from inspect.iscoroutinefunction() because it returns True for generator-based coroutine functions decorated with @coroutine.

But it can not pass inspect.iscoroutinefunction since the returned fn is not an async def function.

Through explicitly defining an async function (wrapper) in

tenacity/tenacity/_asyncio.py

Line 75 in be9bccb

def wraps(self, fn):

one can make it pass both inspect.iscoroutinefunction and asyncio.iscoroutinefunction.

Pull request has been modified.