[FIX] website: edit website.page's menu URL not saving

Before this commit, editing a website.menu (linked to a website.page (m2o))
would not save the URL on the website.page record but only on the
website.menu.
But since the URL retrieved to display the website navbar is:
  1. The website.page url if the menu has a page_id
  2. The website.menu url otherwise
It would never get the edited URL stored on website.menu

addons/website/models/website.py

@@ -866,11 +866,14 @@ class Menu(models.Model):
                 new_menu = self.create({'name': menu['name']})
                 replace_id(mid, new_menu.id)
         for menu in data['data']:
+            menu_id = self.browse(menu['id'])
+            if menu_id.page_id:
+                menu_id.page_id.write({'url': menu['url']})
             # if the url match a website.page, set the m2o relation
             page = self.env['website.page'].search([('url', '=', menu['url'])], limit=1)
             if page:
                 menu['page_id'] = page.id
-            self.browse(menu['id']).write(menu)
+            menu_id.write(menu)
 
         return True