gh-111178: fix UBSan failures for PyBytesObject (#131603)

Objects/bytesobject.c

@@ -2649,15 +2649,16 @@ bytes_hex_impl(PyBytesObject *self, PyObject *sep, int bytes_per_sep)
 }
 
 static PyObject *
-bytes_getnewargs(PyBytesObject *v, PyObject *Py_UNUSED(ignored))
+bytes_getnewargs(PyObject *op, PyObject *Py_UNUSED(dummy))
 {
+    PyBytesObject *v = _PyBytes_CAST(op);
     return Py_BuildValue("(y#)", v->ob_sval, Py_SIZE(v));
 }
 
 
 static PyMethodDef
 bytes_methods[] = {
-    {"__getnewargs__",          (PyCFunction)bytes_getnewargs,  METH_NOARGS},
+    {"__getnewargs__", bytes_getnewargs,  METH_NOARGS},
     BYTES___BYTES___METHODDEF
     {"capitalize", stringlib_capitalize, METH_NOARGS,
      _Py_capitalize__doc__},