[FIX] base : add unlink access to partner manager

To reproduce
============

- make sure to have two contacts with same email (duplicate Mitchell for example)
- in 'Contacts', switch to 'list view', selected any two contacts with the checkboxes, go the the 'Action' menu and select 'Merge'
- Click on 'Skip these contacts', then click on 'Deduplicate the other contacts', then check the 'Email' checkbox and click on 'Merge with manual check'.
- click on 'Skip these contacts'

an Access Error is raised

Purpose
=======

Partner Manager doesn't have the unlink access to `partner.merge.line` model, this access wasn't given because it's often unecessary,
but here it's good example where it's needed.

Specification
=============

to solve the issue we give the unlink access to partner manager.

opw-2851507

closes odoo/odoo#92188

X-original-commit: a6754f35
Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>
Signed-off-by: abla001 <abla@odoo.com>