Fix Y-sort modulate for top-most Y-sorted CanvasItem

(cherry picked from commit bbb2a889d8623114d2b2b659ca764a614f521cf2)

servers/rendering/renderer_canvas_cull.cpp

@@ -313,6 +313,7 @@ void RendererCanvasCull::_cull_canvas_item(Item *p_canvas_item, const Transform2
 			int i = 1;
 			_collect_ysort_children(ci, Transform2D(), p_material_owner, Color(1, 1, 1, 1), child_items, i, p_z);
 			ci->ysort_xform = ci->xform.affine_inverse();
+			ci->ysort_modulate = Color(1, 1, 1, 1);
 
 			SortArray<Item *, ItemPtrSort> sorter;
 			sorter.sort(child_items, child_item_count);