x11-toolkits/gtk-layer-shell: silence gtk3 warning after 4e21a388ba0b
$ nwg-dock
[...]
- (<unknown>:4483): WARNING **: gtk-layer-shell v0.6.0 may not work on GTK v3.24.31. If you experience crashes, check https://github.com/wmww/gtk-layer-shell/blob/master/compatibility.md
PR: 260639