Fix last_return_amount in return invoice templates
CHANGELOG:
### FIXED
- [#584](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/584) Fix last_return_amount in return invoice templates
Edited by Pelayo García
CHANGELOG:
### FIXED
- [#584](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/584) Fix last_return_amount in return invoice templates