In 13.0 66ef641f33 the source field was removed.
This would cause an error when gengo is updating a existing
ir.translation record (eg. if we do two times gengo auto-translations).
opw-2234713
closes #49884
closes odoo/odoo#50001
X-original-commit: 527b3bfb2b17a821d6051a9010ec717a62c7c748
Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>