As already pointed out in the previous testing update thread by another user, using sudo pacman -Syu --asdeps pacman-contrib is not a good idea because it also changes the installation reason of upgraded packages. Before this solution makes its way to the Known issues and solutions section of the next Stable Update thread, in my eyes it’s better to give other instructions like:
First: remove packages requiring pacman-contrib (there may be more than just bmenu and pacui)
sudo pacman -R bmenu pacui
Second: perform the upgrade
sudo pacman -Syu
Third: reinstall previously removed packages
sudo pacman -S bmenu pacui