fix(dotfiles): work around "error" image caused by picom vs xsecurelock
fix(dotfiles): work around "error" image caused by picom vs xsecurelock

As described here:

    https://github.com/google/xsecurelock/issues/97

I was seeing an "INCOMPATIBLE COMPOSITOR, PLEASE FIX!" image on
unlocking the screen. Additionally, after adding and tweaking the
picom.conf file in recent commits, it got worse, showing a strip at the
top corresponding to the dmenu/status bar area all the time, even at the
lock screen.

wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent