tests: unflake t/263-edge-borders.t
tests: unflake t/263-edge-borders.t

stapelberg/i3,i3/i3,cornerman/i3,i3/i3,cornerman/i3,stapelberg/i3,stapelberg/i3,Airblader/i3-original,cornerman/i3,i3/i3,Airblader/i3-original,Airblader/i3-original,cornerman/i3,i3/i3,Airblader/i3,Airblader/i3-original,Airblader/i3,Airblader/i3,stapelberg/i3,Airblader/i3-original,Airblader/i3