Redraw on item list custom bg/fg colour change

(cherry picked from commit 738b0fdae542df469a09451ea5e122b1c2413082)

scene/gui/item_list.cpp

@@ -163,6 +163,7 @@ void ItemList::set_item_custom_bg_color(int p_idx, const Color &p_custom_bg_colo
 	ERR_FAIL_INDEX(p_idx, items.size());
 
 	items.write[p_idx].custom_bg = p_custom_bg_color;
+	update();
 }
 
 Color ItemList::get_item_custom_bg_color(int p_idx) const {
@@ -175,6 +176,7 @@ void ItemList::set_item_custom_fg_color(int p_idx, const Color &p_custom_fg_colo
 	ERR_FAIL_INDEX(p_idx, items.size());
 
 	items.write[p_idx].custom_fg = p_custom_fg_color;
+	update();
 }
 
 Color ItemList::get_item_custom_fg_color(int p_idx) const {