Stub OrderPaymentFinder to return correct object

OrderPaymentFinder was re-fetching the payment object from the database, so the subsequent line that stubs #authorize! on that payment was not being applied to the correct object.

spec/services/checkout/stripe_redirect_spec.rb

@@ -38,6 +38,8 @@ describe Checkout::StripeRedirect do
           it "returns the redirect path" do
             stripe_payment = create(:payment, payment_method_id: payment_method.id)
             order.payments << stripe_payment
+            allow(OrderPaymentFinder).to receive_message_chain(:new, :last_pending_payment).
+              and_return(stripe_payment)
             allow(stripe_payment).to receive(:authorize!) do
               # Authorization moves the payment state from checkout/processing to pending
               stripe_payment.state = 'pending'