[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