Can't use `_typeshed` in TYPE_CHECKING block

Example:

```python
if TYPE_CHECKING:
    from _typeshed import StrPath

def foo(path: StrPath) -> StrPath:
    return path
```

Output (fails a build on read the docs):

```none
WARNING: Failed guarded type import with ModuleNotFoundError("No module named '_typeshed'")
```

Stubs for `_typeshed`: https://github.com/python/typeshed/tree/main/stdlib/_typeshed