Fix regression causing jittery canvas transforms

This PR https://github.com/godotengine/godot/pull/104451 introduced
a tricky regression. Canvas item transforms could risk not being
updated for multiple frames due to the conditional on the line
in this commit. Before the "approx_pos|size_changed" fix, the
transform would get updated incidentally either way. But now there's
a gap where (pos_changed && !size_changed) may not be true for a few
frames and there's nothing else left to trigger a transform update.

The fix is quite simple, for updating the canvas item transform
we remain trigger happy around position changes, but respect the
approx_size_changed.

scene/gui/control.cpp

@@ -1772,7 +1772,7 @@ void Control::_size_changed() {
 			}
 		}
 
-		if (pos_changed && !size_changed) {
+		if (pos_changed && !approx_size_changed) {
 			_update_canvas_item_transform();
 		}