Keys should be materialized if dict is changed in loop

[Pliner]

RuntimeError: dictionary changed size during iteration
  File "aiohttp/web.py", line 431, in _run_app
    await runner.cleanup()
  File "aiohttp/web_runner.py", line 294, in cleanup
    await self._cleanup_server()
  File "aiohttp/web_runner.py", line 381, in _cleanup_server
    await self._app.cleanup()
  File "aiohttp/web_app.py", line 430, in cleanup
    await self.on_cleanup.send(self)
  File "aiohttp/signals.py", line 34, in send
    await receiver(*args, **kwargs)  # type: ignore
  File "aiohttp/web_app.py", line 550, in _on_cleanup
    raise errors[0]
  File "aiohttp/web_app.py", line 541, in _on_cleanup
    await it.__anext__()
  File "app.py", line 695, in configure_http_client
    await resolver.close()
  File "aio_request/aiohttp.py", line 62, in close
    await self._task
  File "aio_request/aiohttp.py", line 72, in _resolve
    for key in self._results.keys():