bpo-33644: Fix signatures of tp_finalize handlers in testing code. (GH-7111)

diff --git a/Modules/xxlimited.c b/Modules/xxlimited.c
index 5041ac8..5586989 100644
--- a/Modules/xxlimited.c
+++ b/Modules/xxlimited.c
@@ -47,11 +47,10 @@
     return 0;
 }
 
-static int
+static void
 Xxo_finalize(XxoObject *self)
 {
     Py_CLEAR(self->x_attr);
-    return 0;
 }
 
 static PyObject *