[FIX] website_crm: fix access error for users without CRM rights

1. Backport of [1].
2. Steps to reproduce:
- Install website_crm
- Connect as Admin and remove the sales rights for Demo
- Check the website on a private window (to create an anonymous visit)
- Connect as Demo on the normal window
- Go to Website > Reporting > Visitors
=> It triggers an access error due to lead_ids being restricted to
sales_team.group_sale_salesman.
(Note: the error sometimes isn't triggered at that point. In that case,
click on the visitor: the same error will trigger.)

Considering the computed field doesn't do anything critical as it just
retrieves the email and phone number, the restriction is overridden on
the field.

[1]: https://github.com/odoo/odoo/commit/7de453477d7c23e607a15e0d60613080857e3371



opw-3475301

closes odoo/odoo#136194

X-original-commit: 5ba09c2c
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>