bpo-42233: Correctly repr GenericAlias when used with typing module (GH-23081)

Noticed by @serhiy-storchaka in the bpo.  `typing`'s types were not showing the parameterized generic. 
Eg. previously:
```python
>>> typing.Union[dict[str, float], list[int]]
'typing.Union[dict, list]'
```
Now:
```python
>>> typing.Union[dict[str, float], list[int]]
'typing.Union[dict[str, float], list[int]]'
```

Automerge-Triggered-By: GH:gvanrossum