[FIX] calendar: wrong user updated when setting last notif ack

Since commit 91560fae, we are using sudo to write
calendar_last_notif_ack, but we need to update the real partner stored
in the context.

opw-2133566

closes odoo/odoo#41976

X-original-commit: 4d6416db
Signed-off-by: Alex Tuyls <alt-odoo@users.noreply.github.com>