Add Evan Welsh as a maintainer.

I'd like to review and merge in the libhandy cleanups (!58 (closed), !60 (closed)) and drop extension support (!50 (merged)) for GNOME Tweaks 40 given the success of the official Extensions app.

On 3.38, Tweaks 3.34 is at least partially broken for many users on normal scaling which ideally should be resolved soon.