[FIX] calendar: wrong timezone in sms template

Issue :
- When sending an sms reminder by cron user, `_get_display_time` is
used which always uses Odoobot (cron user) timezone regardless of the
partner timezone

Fix:
- use `partner_id.tz` instead of Odoobot

OPW-2991624

closes odoo/odoo#100733

Signed-off-by: Mohamed Megahed Abbas Megahed SALLAM (mome) <mome@odoo.com>