prefs-dialog: Fix the indentation

This allows the previous commit to be easier to review by keeping its
focus on what it actually changes.
3 jobs for wip/aplazas/preferences in 10 minutes and 47 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #227904
flatpak

00:10:10

 
  Deploy
passed #227905
review

00:00:36

manual #227906
allowed to fail manual
stop_review