Use set instead of WeakSet in TaskGroup

[heckad]

Fix bug with tasks leaking from a TaskGroup.

[achimnol]

Um.. could you explain more context on this change?
Because weakref.WeakSet is a deliberate choice to prevent memory leaks by allowing task objects garbage-collected right after they finish.

[heckad]

Sorry for the late response. We just updated to python3.11 to solve the problem but here's a minimal MRE

import asyncio
import gc
import weakref

import aiotools


all_features = weakref.WeakSet()


async def inf_loop(future):
    while True:
        print("Message")
        await future


async def inner_scope(tg: aiotools.TaskGroup):
    future = asyncio.Future()

    tg.create_task(inf_loop(future))

    all_features.add(future)


async def main():
    try:
        async with aiotools.TaskGroup() as tg:
            await inner_scope(tg)
            await asyncio.sleep(1)
            gc.collect()
            print("collected")

            raise asyncio.CancelledError
    except asyncio.CancelledError:
        pass

asyncio.run(main(), debug=True)

With standard task group all good but on python3.10 with task group from aiotools we got
Task was destroyed but it is pending!