Fix/contract lines tree contract view form

CHANGELOG:

### Fix
- [#1031](https://git.coopdevs.org/coopdevs/som-connexio/odoo-somconnexio/-/merge_requests/1031) Fix ContractLines view inside the Contract view.

Related card: https://trello.com/c/0HawzT1c/1583-revisar-columnes-l%C3%ADnies-de-contracte

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