tests: remove warning on Element.getchildren() (#41302)

tests/test_api.py

@@ -158,7 +158,7 @@ def test_binary_data(app, partner_southpark, cut_kevin_uuid, acl):
     assert resp.headers.get('Content-Type') == content_type
     xml_data = etree.fromstring(resp.content)
     assert xml_data.tag == 'friends'
-    assert len(xml_data.getchildren()) == 4
+    assert len(list(xml_data)) == 4
 
     # test update by changing format
     payload = {"friends": [{"name": "Token", "age": 10}, {"name": "Kenny", "age": 10}]}