Add missing license header to the test scheduling history retriever script

scripts/test_scheduling_history_retriever.py

@@ -1,4 +1,7 @@
 # -*- coding: utf-8 -*-
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this file,
+# You can obtain one at http://mozilla.org/MPL/2.0/.
 
 import argparse
 import json