Original PR description

Currently, a traceback occurs when the user tries to duplicate multiple pos payment methods.

To reproduce this issue:

1) Install Point of Sale
2) Try to duplicate multiple payment methods from the POS configuration

Error:- 
```
ValueError: Expected singleton: account.journal(14, 18)
```

This is because of the changes from the recent commit https://github.com/odoo/odoo/pull/175530/commits/0fbd47bdd2fe06feda7df747e8560b810a666386

In `copy` method, when multiple records are duplicated it executed the method at multiple times.
 so `self` should have a single record at a time.

From the `saas-17.2`, the `copy` method changes to `copy_data`, 
So it is executed at a time when the `self` having multiple recordsets.

This leads to a traceback as `self.journal_id.type` is used.

https://github.com/odoo/odoo/blob/88604332ae37d75c1435a298319a378841abf25a/addons/point_of_sale/models/pos_payment_method.py#L166-L168

sentry-5790593911