[FIX] google_calendar: correct use of datetime object
[FIX] google_calendar: correct use of datetime object

Remove useless .split calls now that we have datetime objects
Avoid manipulating strings

Fixes odoo/odoo#27453

closes odoo/odoo#27521
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo