support python 3.12 type alias syntax

python 3.12 introduced new syntax for type aliases:

```py
type Foo = int
```

this is currently highlighted incorrectly:

![image](https://github.com/MagicStack/MagicPython/assets/57028336/6e7d87af-ecf8-4f60-91c6-9a0dcb99c772)

(the `type` keyword should be blue and the `Foo` name should be green)

related: #262