Ensure the callable is an async def.

def _async_callable(func):
    """Ensure the callable is an async def."""
    if isinstance(func, types.CoroutineType):

        return func

    @functools.wraps(func)
    async def _async_def_wrapper(*args, **kwargs):
        """Wrap a a sync callable in an async def."""
        return func(*args, **kwargs)

    return _async_def_wrapper