[FIX] google_calendar: use the request root URL for the `redirect_uri`

Before this commit: if a different `web.base.url` is set with
`web.base.url.freeze`, during the first synchronization of Google
calendar it will show a mismatch URL error. The problem is that we
send the `redirect_uri` based on the `web.base.url` in the
`_get_authorize_uri` function.

The solution is to use the request root URL instead.

opw-3101741

closes odoo/odoo#111336

Signed-off-by: Arnaud Joset <arj@odoo.com>