window: Don't try to focus unmanaging windows

GNOME/mutter!307
2 jobs for workspace-use-focusable-ancestor in 4 minutes and 58 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #215420
build-mutter

00:01:49

 
  Test
passed #215421
test-mutter

00:03:09