Fix compilation on Windows

Objects/bytearrayobject.c

@@ -636,6 +636,7 @@ bytearray_ass_subscript(PyByteArrayObject *self, PyObject *index, PyObject *valu
         needed = 0;
     }
     else if (values == (PyObject *)self || !PyByteArray_Check(values)) {
+        int err;
         if (PyNumber_Check(values) || PyUnicode_Check(values)) {
             PyErr_SetString(PyExc_TypeError,
                             "can assign only bytes, buffers, or iterables "
@@ -643,7 +644,6 @@ bytearray_ass_subscript(PyByteArrayObject *self, PyObject *index, PyObject *valu
             return -1;
         }
         /* Make a copy and call this function recursively */
-        int err;
         values = PyByteArray_FromObject(values);
         if (values == NULL)
             return -1;