[FIX] website_crm_partner_assign: modify lead

- As admin, create an opportunity
- Under the tab Assigned partner set the portal user
- As portal user go to My account > My opportunities > Edit opportunity
- Change something

Confirm button doesn't work. In fact, an access error is raised silently
in the JS console.

The issue is raised in `update_lead_portal`, at `lead.activity_ids...`.
This is because the field `activity_ids` has
`groups="base.group_user"`.

opw-1817935
opw-1818629

addons/website_crm_partner_assign/models/crm_lead.py

@@ -233,7 +233,7 @@ class CrmLead(models.Model):
             # will be modified by the portal form. If no activity exist we create a new one instead
             # that we assign to the portal user.
 
-            user_activity = lead.activity_ids.filtered(lambda activity: activity.user_id == self.env.user)[:1]
+            user_activity = lead.sudo().activity_ids.filtered(lambda activity: activity.user_id == self.env.user)[:1]
             if values['activity_date_deadline']:
                 if user_activity:
                     user_activity.sudo().write({