Steps to reproduce:
------------------------
1. Install the Helpdesk.
2. Go to Settings → Technical → Sequences and set the next number to 100.
3. Create a ticket and send a message using the "Helpdesk: Ticket Received"
mail template; Observe that the correct reference (100) is used.
(Open the full composer to use "Load template")
4. Now send a message using the "Helpdesk: Ticket Closed" mail template
and Observe that it displays the database ID (e.g., 1) instead of the reference.


Cause:
------
`new_ticket_request_email_template` uses the ticket reference(`object.ticket_ref`) correctly.
https://github.com/odoo/enterprise/blob/d39e291ba89ad018ba6f5f9591d280a834822f27/helpdesk/data/mail_template_data.xml#L18-L19

However, the `solved_ticket_request_email_template` uses the database ID (`object.id`)
instead of the actual ticket reference (`object.ticket_ref`), leading to inconsistent references
in customer communications.

related commit: 3ed5273

Solution:
---------
Update `solved_ticket_request_email_template` to use `object.ticket_ref` instead of `object.id`

opw-6087466

Forward-Port-Of: odoo/enterprise#113932