[FIX] web, website: fix menu auto hide in edit mode

Steps to reproduce:

- Go to Website > Add menu items to activate the "auto-hide" (to set the
overflowing menu items in a "+" dropdown).
- Go to "edit" mode > While resizing the window width, the "auto-hide"
menu adaptation is disabled, and overflowing menu items are visible.

The goal of this commit is to fix the behaviour described above (and
potentially, issues that can result from the editor's "unbreakable"
rollbacks on top menu) by preventing the unbreakable mechanism from
detecting header changes and cancelling the auto-hide updates.

Related to opw-3484742

closes odoo/odoo#134185

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>