Fix tuple subclass test

Author: msimacek

graalpython/com.oracle.graal.python.test/src/tests/cpyext/__init__.py

@@ -490,7 +490,7 @@ def CPyExtType(name, code, **kwargs):
     {includes}
 
     typedef struct {{
-        PyObject_HEAD;
+        {struct_base};
         {cmembers}
     }} {name}Object;
 
@@ -636,6 +636,7 @@ def CPyExtType(name, code, **kwargs):
     kwargs.setdefault("tp_free", "PyObject_Del")
     kwargs.setdefault("cmembers", "")
     kwargs.setdefault("includes", "")
+    kwargs.setdefault("struct_base", "PyObject_HEAD")
     c_source = UnseenFormatter().format(template, **kwargs)
 
     source_file = "%s/%s.c" % (__dir__, name)

graalpython/com.oracle.graal.python.test/src/tests/cpyext/test_tuple.py

@@ -78,6 +78,7 @@ def __repr__(self):
             return result;
        }
     """,
+    struct_base='PyTupleObject tuple',
     tp_base='&PyTuple_Type',
     tp_new='tuple_subclass_new',
     tp_alloc='0',