bpo-40462: Fix typo in test_json (GH-20094)

diff --git a/Lib/test/test_json/test_recursion.py b/Lib/test/test_json/test_recursion.py
index 877dc44..543c628 100644
--- a/Lib/test/test_json/test_recursion.py
+++ b/Lib/test/test_json/test_recursion.py
@@ -52,7 +52,7 @@
                         return [JSONTestObject]
                     else:
                         return 'JSONTestObject'
-                return pyjson.JSONEncoder.default(o)
+                return self.json.JSONEncoder.default(o)
 
         enc = RecursiveJSONEncoder()
         self.assertEqual(enc.encode(JSONTestObject), '"JSONTestObject"')