[FIX] account_qr_code_sepa : Fixed format of 'amount of transfer' not correct in QR-code

Reproduce :
- Create an invoice with a sepa QR-code.

Result :
  When reading the QR-code, German banks assume the fisrt 3 characters are the currency name/code, so the first 3 digits of the amount are cut from this amount.

Solution :
  The amount now starts with the currency name/code (3 letters), as prescribed by EPC norms.

opw-2591454

closes odoo/odoo#75816

Signed-off-by: Quentin De Paoli (qdp) <qdp@openerp.com>