Use partner to render mass_mailing test
CHANGELOG:
### CHANGED
- [#825](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/825) Use partner to render mass_mailing test
Edited by Pelayo García
CHANGELOG:
### CHANGED
- [#825](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/825) Use partner to render mass_mailing test