`SPLIT_ALL_COMMA_SEPARATED_VALUES` not working for nested lists

Hello,

I have some code that looks like this:

```
class TopLevelClass:

def __init__(
self,
arg_1: Callable[[list_item_1],
list_item_2] = default_list_item,
arg_2: Callable[[str], Optional[list_item_3]] = default_list_item_1,

...
```

I expected turning `SPLIT_ALL_COMMA_SEPARATED_VALUES = True` would put the list items in the `arg_1` to be put on separate lines but this formatting remains. Is there a good way to debug how yapf is determining the new lines?