[#3688] Fix existing test after update

src/openforms/registrations/contrib/objects_api/tests/test_update_payment_status_v1.py

@@ -59,6 +59,7 @@ def test_update_payment_status(self, m):
 
  m.patch(
  "https://objecten.nl/api/v1/objects/111-222-333",
+ json={}, # Unused in our case, but required as .json() is called on the response
  status_code=200,
  )
 
@@ -117,11 +118,11 @@ def test_template_overwritten_through_options(self, m):
 
  m.patch(
  "https://objecten.nl/api/v1/objects/111-222-333",
+ json={}, # Unused in our case, but required as .json() is called on the response
  status_code=200,
  )
 
  plugin = ObjectsAPIRegistration(PLUGIN_IDENTIFIER)
-
  with freeze_time("2020-02-02"):
  with patch(
  "openforms.registrations.contrib.objects_api.models.ObjectsAPIConfig.get_solo",
@@ -190,6 +191,7 @@ def test_no_template_specified(self, m):
 
  m.patch(
  "https://objecten.nl/api/v1/objects/111-222-333",
+ json={}, # Unused in our case, but required as .json() is called on the response
  status_code=200,
  )