[Python 3.9 compat] type is now subscriptable.

Since Python 3.9, `type` is made subscriptable by Objects/abstract.c (python/cpython@48b069a), to allow, for example, `type[int]`.

```python
print(type[int])
```

which give:
```
test.py:10:6: E1136: Value 'type' is unsubscriptable (unsubscriptable-object)
```

while the code works.

Related to #3890.
See also #3882.
