Fix expected singleton error
CHANGELOG:
### Fix
- [#659](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/659) Fix expected singleton error from contract `_get_is_broadband
Edited by Pelayo García
CHANGELOG:
### Fix
- [#659](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/659) Fix expected singleton error from contract `_get_is_broadband