Error with `TypeVarTuple` typing

Hello!

I'm using mutmut for my mutation tests but I get this **KeyError** error with python 3.11 TypeVarTuple typing syntax :

Example of code:
```python
T = TypeVar('T')
Ts = TypeVarTuple('Ts')

def append(tpl: tuple[*Ts], value: T) -> tuple[*Ts, T]:
return tpl + (value,)
```

result :

**_KeyError: ReservedString(*)_**

This it because of the `*` in the function signature

Thx ;)