[FIX] event: fix traceback while downloading ics file

Currently while downloading ics for an event, it gives
traceback due to improper handling of kwargs.

It was introduced from https://github.com/odoo/odoo/commit/a03faab03fdf8a164c2f1298cc138b3fa83b0bea



This commit fixes the issue by properly handling
kwargs in the method definition.

task-1938637

closes odoo/odoo#32750

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>