Fix issue with async definitions failing the type checker

[meadsteve]

For this code:

    @dependency_definition(container)
    async def my_constructor() -> MyComplexDep:
        return MyComplexDep(some_number=5)

    assert (await container[Awaitable[MyComplexDep]]) == MyComplexDep(some_number=5)

mypy raises these errors:

 error: Only concrete class can be given where "Type[Awaitable[MyComplexDep]]" is expected

[meadsteve]

Another https://github.com/python/mypy/issues/5374 probably

[thiromi]

I'm facing the exactly same issue 😞