panic: `no entry found for key` with stringified set comprehension in type expression

### Summary

ty crashes when checking this fuzzed code:

```python
x: "f'{1 if 1 else 1}'"
```

```
error[panic]: Panicked at crates/ty_python_semantic/src/types/infer/builder.rs:8187:28 when checking `/home/user/a.py`: `no entry found for key`
```

### Version

5e31bc93 w/ astral-sh/ruff@bc8efa2fd86