Ensure cooperator is true when validating a SR
CHANGELOG:
### Fix
- [#759](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/759) Ensure partner's cooperator flag is set to True when validating a SR from them
Related card: https://trello.com/c/lMOrWNvJ/1156-capital-social-pagat-i-encara-consten-com-a-candidata-a-s%C3%B2cia