[FIX] payment_stripe: validation operations treated incorrectly

When saving a payment method from the `my/payment_method` page
validation is used as the type of operation. In the present
validation operations were incorrectly filtered and treated as a
payment.
After this commit validation operations are processed in the
`_stripe_create_checkout_session` function as it should.

Task - 3001168

closes odoo/odoo#101923

X-original-commit: 7f371db1af160a5e89f9476540aee35f79769068
Signed-off-by: Antoine Vandevenne (anv) <anv@odoo.com>

addons/payment_stripe/models/payment_transaction.py

@@ -35,7 +35,7 @@ class PaymentTransaction(models.Model):
         if self.provider_code != 'stripe' or self.operation == 'online_token':
             return res
 
-        if self.operation == 'online_redirect':
+        if self.operation in ['online_redirect', 'validation']:
             checkout_session = self._stripe_create_checkout_session()
             return {
                 'publishable_key': stripe_utils.get_publishable_key(self.provider_id),