Force attachment conv to str
CHANGELOG:
### Fix
- [#575](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/575) Force attachment conversion to str it is bytes
Edited by Pelayo García
CHANGELOG:
### Fix
- [#575](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/575) Force attachment conversion to str it is bytes