[FIX] payment_payumoney: update sandbox env url

before this commit: it gives error when we redirect to payumoney site

after this commit: payment testing in payumoney is working as expected

closes odoo/odoo#36764

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

addons/payment_payumoney/models/payment.py

@@ -25,7 +25,7 @@ class PaymentAcquirerPayumoney(models.Model):
         if environment == 'prod':
             return {'payumoney_form_url': 'https://secure.payu.in/_payment'}
         else:
-            return {'payumoney_form_url': 'https://test.payu.in/_payment'}
+            return {'payumoney_form_url': 'https://sandboxsecure.payu.in/_payment'}
 
     def _payumoney_generate_sign(self, inout, values):
         """ Generate the shasign for incoming or outgoing communications.