CI: add empty line in `no-bool-in-generic` to avoid `black` complaining
*No reference issues (I ran into this during another contribution).*

Why is this needed? For instance if I used `bool` in generic, this hook will delete the last empty line. Then if I add the changes and commit again, `black` will complain about it. Well then if you add the changes and commit again everything will be fine, but I just think it would be better to avoid such conflict.

Or did I miss something? @mroeschke Can you show a commit where this happened? Does this suffice? @mroeschke

https://github.com/pandas-dev/pandas/assets/108576690/858ec0dc-b550-4e65-93fe-55d2ec53bd53
 Ah great thanks for that demonstration 👍 