No narrowing on `is not None` when using NoneType in a type annotation

### Describe the Bug

Reproducer:

```
from types import NoneType

N = NoneType

def test(x: int | N):
  assert x is not None
  reveal_type(x)  # => NoneType | int
```

This looks like `N` is not normalized to `None` in the type of `x`.

### Sandbox Link

_No response_

### (Only applicable for extension issues) IDE Information

_No response_