[fix] page item submenu (#1461)

This PR fixes a bug that would effect the page item submenu. With the
`useMenuIsOpen` hook, it's important that multiple menus have unique
ids. In this case each page was using `page sub menu` and so each open
menu would be closed by the not-open menu effects.

### Change Type

- [x] `patch` — Bug Fix

### Test Plan

1. Create two pages
2. Open the submenus on each page

packages/ui/src/lib/components/PageMenu/PageItemSubmenu.tsx

@@ -44,7 +44,7 @@ export const PageItemSubmenu = track(function PageItemSubmenu({
 	}, [app, item])
 
 	return (
-		<M.Root id="page item submenu">
+		<M.Root id={`page item submenu ${index}`}>
 			<M.Trigger>
 				<Button title={msg('page-menu.submenu.title')} icon="dots-vertical" />
 			</M.Trigger>