This is now fixed in main thanks to bpo-46644:

```
>>> get_type_hints(Foo)
{'attr': dataclasses.InitVar[int]}
```

We're not backporting that change to the bugfix branches. If we want to fix this issue in 3.10 and 3.9, we'll have to add a `__call__` method to `InitVar`. My inclination is that that's not worth it.