fix: 'TopBarItem' object does not support item assignment #17926 (#17927)

TypeError: 'TopBarItem' object does not support item assignment
(cherry picked from commit 9358655ae2)

Co-authored-by: Faris Ansari <netchampfaris@users.noreply.github.com>

frappe/website/doctype/website_settings/website_settings.py

@@ -218,7 +218,7 @@ def modify_header_footer_items(items: list):
 				continue
 
 			if not top_bar_item.get("child_items"):
-				top_bar_item["child_items"] = []
+				top_bar_item.child_items = []
 
 			top_bar_item.child_items.append(item)
 			break