[FIX] website: state not saved for accordion snippet

Before this commit, the states (collapsed/not collapsed) of the tabs
of the accordion snippet were not saved if it was the only changement
in edit mode.

After this commit, we trigger a content change when the states of the
tabs is changed.

task-2442237

closes odoo/odoo#67211

Signed-off-by: Jérémy Kersten (jke) <jke@openerp.com>