[FIX] crm: allow regular salesman to convert and merge opportunities

If an internal user does not belong to Sales / Administrator group, and wants
to convert a lead into an opportunity, he will face an access rights error if
another lead exists with the same email because we are trying to merge them.
We should allow him to convert and merge them without error.

closes odoo/odoo#75216

Signed-off-by: Alex Tuyls <alt-odoo@users.noreply.github.com>

addons/crm/wizard/crm_lead_to_opportunity.py

@@ -136,7 +136,7 @@ class Lead2OpportunityPartner(models.TransientModel):
                     'user_id': self.user_id.id,
                     'team_id': self.team_id.id,
                 })
-        (to_merge - result_opportunity).unlink()
+        (to_merge - result_opportunity).sudo().unlink()
         return result_opportunity
 
     def _action_convert(self):