Run upload_to_google_storage.py with Python 3

Change-Id: I7271280deb09c9675567f3dd255e809da19619b7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3484977
Auto-Submit: David Benjamin <davidben@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>

upload_to_google_storage.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.