clutter/actor: Don't notify resource-scale update when using global scale

When using the global resource scale, the actors are notified for scale changes
as soon it happens, while it's not needed to notify the actors again when
the real resource scale gets computed.

GNOME/mutter!493
3 jobs for !493 with resource-scale-computation-optimizations in 5 minutes and 22 seconds (queued for 1 second)
latest detached
Status Job ID Name Coverage
  Review
passed #244559
check-commit-log

00:00:50

 
  Build
passed #244560
build-mutter

00:01:33

 
  Test
passed #244561
test-mutter

00:02:59