Fix repeated import case
CHANGELOG:
### FIXED
- [#618](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/618) Email Account Payment Return Gateway now ignores already processed return files.
Related card: https://trello.com/c/W6DGz4aP/922-borrar-correos-devoluciones-de-banco-que-ya-est%C3%A1n-procesados
⚠ Needs https://git.coopdevs.org/coopdevs/odoo/inventories/odoo-somconnexio-inventory/-/merge_requests/71 ⚠
Edited by César López Ramírez