Arrow keys cannot change brightness in the popup

If you click on the panel icon and/or even click on the brightness sliders in the resulting popup, the arrow keys do not work to change the brightness (ideally in smaller increments than when using the scroll wheel on hover for changing the brightness)

This is something supported in the likes of at least the Cinnamon desktop environment.

For reference, the audio popup has the same issue but supposedly doesn't actually share any code; you can refer to the video demonstration over in the corresponding issue - I just kind of forgot to report the issue over here with this package...: panel-plugins/xfce4-pulseaudio-plugin#121

(for that reason, the last time I tested this was admittedly 4 months ago on Xubuntu 25.10 daily build 2025-06-12 with Xfce 4.20.2, but it looks like 99% of the commits for xfce4-power-manager between now and June are almost all just translation updates, and the few that aren't don't seem to be relevant to this issue anyway, so... but if it's strongly preferred, I can test again using the latest openSUSE Tumbleweed which seems to keep much more up-to-date on using rather cutting-edge versions of Xfce)