ban implicit casting of `Any` with explicit annotation

```py
# third_party.py
def foo() -> Any: ...
```
```py
# my.py
some_list: list[int] = third_party.foo() # that's okay?
```

The issue provides only two Python snippets and does not name an implementation file, entry point, or test. First clarify whether the annotated assignment should be rejected when the called function returns Any, then locate the checker logic and add tests covering the shown third_party.foo and my.py example; done means the intended diagnostic behavior is specified and verified.

Written by the indexing model from the issue text.