This was discovered when looking at [#122332](https://github.com/python/cpython/issues/122332) on CPython. With 3.12's new `asyncio.eager_task_factory`, `Task.get_coro()` is able to return `None` (see [here](https://docs.python.org/3/library/asyncio-task.html#asyncio.Task.get_coro)). This needs to be reflected in the stubs.
