Fine-grained: Nested class causes hang

This fine-grained incremental mode test case hangs:

```
[case testRefreshNestedClassWithSelfReference]
import a
[file a.py]
import b

def f(self) -> None:
    b.y
    class C:
        z: C
[file b.py]
y = 0
[file b.py.2]
y = ''
[out]
==
```