As usually with GObject setters, we should check whether the property
actually changed before setting the value and notifying the property. So
check whether the title or description text actually changed before
setting it.
This fixes a bug which makes the title flicker and change its size,
because when updating the title we remove the "leightweight" css class
and reapply it inside a later, which makes the title appear larger for
one frame.
Fixes https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/2574https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1336