[FIX] calendar: allow disabling bus notification in views

Before this commit, when the user group calendar.event by private fields,
a bus notification is sent to exlain that private fields can't be displayed
and the private events are hidden from the result.

It was an issue in some views where group by private fields was used
by default and multiple notifications were displayed.

closes odoo/odoo#127203

Taskid: 3328718
Signed-off-by: Arnaud Joset (arj) <arj@odoo.com>