[FIX] account_edi: file validation while uploading

This issue was caught in sentry.
When we try to create or update an invoice by uploading an `.xlsx` attachment,
it raises an Error as it will go to convert it into XML tree because the
concerned LOC will check `xml` in `mimetype` of attachment which is
`application/vnd.openxmlformats-officedocument.spreadsheetml.sheet`.

sentry-3929855076

closes odoo/odoo#115653

Signed-off-by: William André (wan) <wan@odoo.com>