[ty] Fix class literal subtyping with object fallback (#20521)

## Summary

@ibraheemdev notes this example failed

```py
from typing import Callable

class X:
    ...

def f(callable: Callable[[], X]) -> X:
    return callable()

x = f(X)
```

Resolves https://github.com/astral-sh/ty/issues/1210

The issue was that we set the `Self` to the class type instead of the
instance type of the class.

## Test Plan

Fix tests in `is_subtype_of.md`

crates/ty_python_semantic/src/types/class.rs

@@ -1185,7 +1185,7 @@ impl<'db> ClassType<'db> {
                 if let Place::Type(Type::FunctionLiteral(new_function), _) = new_function_symbol {
                     Type::Callable(
                         new_function
-                            .into_bound_method_type(db, self_ty)
+                            .into_bound_method_type(db, correct_return_type)
                             .into_callable_type(db),
                     )
                 } else {