fix register tz issue

tournaments/services/tournament_registration.py

@@ -47,7 +47,9 @@ class RegistrationCartManager:
 
         expiry_str = self.session['registration_cart_expiry']
         try:
-            expiry = datetime.datetime.fromisoformat(expiry_str)
+            expiry = parse_datetime(expiry_str)
+            if expiry is None:
+                return True
             return timezone.now() > expiry
         except (ValueError, TypeError):
             return True