Fix memory leaks on channel close

[mosquito]

Fixes #490

leaks_test.py

import asyncio
import logging

import aiomisc
from aiomisc.service.tracer import MemoryTracer
from aio_pika import connect_robust

async def main():
    logging.basicConfig(level=logging.DEBUG)

    counter = 0
    while True:
        connect = await connect_robust()
        channel = await connect.channel()
        await asyncio.sleep(0.001)
        await channel.close()
        await connect.close()
        counter += 1

        if not counter % 100:
            logging.info("%d Connections done", counter)

aiomisc.run(main(), MemoryTracer(), log_format="rich")