use vpython3 in run_gtest_angle_test.py

Bug: chromium:1275016
Change-Id: I5de36e1e89b3b657df0b6c302801303539f4fc90
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3394467
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>

scripts/run_gtest_angle_test.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env vpython3
 # Copyright 2020 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.