Ensure a folder's sidebar children are re-added when its type changes.

Fixes issue #11.
5 jobs for wip/11-special-folder-children in 11 minutes and 21 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #57214
deb-package

00:02:24

passed #57212
fedora

00:06:13

passed #57668
flatpack-package

00:05:06

passed #57213
ubuntu

00:02:03

failed #57215
flatpack-package

00:06:49