Fix return from PyException_SetTraceback

Author: msimacek

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/modules/cext/PythonCextErrBuiltins.java

@@ -631,7 +631,7 @@ abstract static class PyException_SetTraceback extends CApiBinaryBuiltinNode {
         Object setTraceback(Object exc, Object traceback,
                         @Cached PyObjectSetAttr setAttrNode) {
             setAttrNode.execute(exc, T___TRACEBACK__, traceback);
-            return PNone.NONE;
+            return 0;
         }
     }
 }