`[name-defined]` when PEP-696 type var uses another type var as default

```python
class A[X, Y = X]: ...

print(A.__parameters__)
print(A.__parameters__[1].__default__)
```

This in runtime produces:

```python
(X, Y)
X
```

While `mypy@1.18.1` produces on python 3.13:

```
ex.py:1: error: Name "X" is not defined  [name-defined]
```

which just the default configuration.