[FIX] mail: correctly give tracking values to notification template

Notification template has been converted into QWeb at commit 0f301bec25.
A variable renaming has not been correctly propagated, leading to
tracking values not being displayed in notification emails. This
commit fixes that.

addons/mail/models/res_partner.py

@@ -85,7 +85,7 @@ class Partner(models.Model):
             'model_name': model_name,
             'record': record,
             'record_name': record_name,
-            'tracking': tracking,
+            'tracking_values': tracking,
             'is_discussion': is_discussion,
             'subtype': message.subtype_id,
         }