Fix/coop candidate can sponsor

CHANGELOG:

### Changed
- [#680](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/680) Allow coop candidates to sponsor.

Related card: https://trello.com/c/bRTZDiwP/1014-els-candidats-a-socia-han-de-poder-apadrinar

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