Reset old context when opening new sub req form

CHANGELOG:

### FIXED
- [#809](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/809) Fix concurrency error when validating sub req from wizard

Related card: https://trello.com/c/eO2JPT9c/983-validaci%C3%B3-convertir-a-soci

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