Change the resource prefix to /org/gnome/Manette

This is shorter and looks nicer than /org/gnome/aplazas/libmanette.
3 jobs for master in 5 minutes and 4 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #643652
check-api-visibility

00:00:25

passed #643654
fedora

00:05:04

passed #643653
flatpak
flatpak

00:01:10