[FIX] mail: multi-company access to TZ

- Create 2 Companies A & B
- Set User B in Company B
- Record some `mail.activity` for User B on a lead belonging to Company
  B.
- With a manager user in Company A, go to Kanban view of leads and
  remove filters => all leads, including leads in Company B, are
  displayed

An access error occurs.

`read_progress_bar` method, tries to access the field `activity_state`
which is: `states = record.activity_ids.mapped('state')`. The state of
a `mail.activity` is using the tz of the partner. To read the
`activity_state` of a lead, one needs to access
`record.activity_ids.user_id.partner_id.tz`
=> multi-company security rules raised

opw: 1850984, 1859470

addons/mail/models/mail_activity.py

@@ -113,9 +113,10 @@ class MailActivity(models.Model):
 
         for record in self.filtered(lambda activity: activity.date_deadline):
             today = today_default
-            if record.user_id.tz:
+            tz = record.user_id.sudo().tz
+            if tz:
                 today_utc = pytz.UTC.localize(datetime.utcnow())
-                today_tz = today_utc.astimezone(pytz.timezone(record.user_id.tz))
+                today_tz = today_utc.astimezone(pytz.timezone(tz))
                 today = date(year=today_tz.year, month=today_tz.month, day=today_tz.day)
 
             date_deadline = fields.Date.from_string(record.date_deadline)