[FIX] calendar: Dont send mail to attendees when the event date is past

Issue

    - Install "Calender"
    - Install "Google Calendar"
    - Try to sync google in "Calendar"

    Every created events will trigger the sending mail to attendees
    even if the event date is past

Cause

    'events' was not filtered

Solution

    Filter 'events' to get all the events that have not yet happened

opw-2358123

closes odoo/odoo#60379

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>