Add test for __new__ not being descriptor

Author: msimacek

graalpython/com.oracle.graal.python.test/src/tests/test_class.py

@@ -46,3 +46,9 @@ def inner(other):
             return inner
 
     assert A() == A()
+
+
+def test_new_not_descriptor():
+    class C:
+        __new__ = str
+    assert C() == str(C)