[FIX] payment_stripe_sca: faulty fix

Commit 83bb8224 introduced some fixes to make a few test of the
normal stripe module work, but unfortunately introduced a bug in
the process.

The reference we want to find the transaction is *not* contained
in the metadata dict but indeed in the reference param of the whole
response dict. Unfortunately, even the fallback of the get call did
not work - the metadata dict is still there, we just don't use it
anymore...

opw-2080651

closes odoo/odoo#38989

Signed-off-by: Damien Bouvy (dbo) <dbo@odoo.com>

addons/payment_stripe_sca/models/payment.py

@@ -237,7 +237,7 @@ class PaymentTransactionStripeSCA(models.Model):
     def _stripe_form_get_tx_from_data(self, data):
         """ Given a data dict coming from stripe, verify it and find the related
         transaction record. """
-        reference = data.get('metadata', data).get("reference")
+        reference = data.get("reference")
         if not reference:
             stripe_error = data.get("error", {}).get("message", "")
             _logger.error(