Equalize dimensions of ws switcher popup boxes

GNOME/gnome-shell#1243
4 jobs for !532 with ws-switcher-box-fix in 4 minutes and 22 seconds (queued for 1 second)
latest detached
Status Job ID Name Coverage
  Review
passed #291230
check_commit_log

00:00:21

 
  Build
passed #291231
build

00:02:54

 
  Test
passed #291232
test

00:01:05

passed #291233
test-pot

00:01:05