Specify python3 for run_with_dummy_home.py's shebang

This would no longer run when invoked directly on machines whose
unversioned python package has been removed.

We now specify the version, and since this doesn't appear to have
any issues running under python3, we use python3.

Bug: 1275016
Change-Id: Iba3dffe2d27ee1cd0d786d6ae2e37fcc38d9dd15
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3465374
Commit-Queue: Kevin McNee <[email protected]>
Auto-Submit: Kevin McNee <[email protected]>
Reviewed-by: John Chen <[email protected]>
Commit-Queue: John Chen <[email protected]>
Cr-Commit-Position: refs/heads/main@{#971311}
diff --git a/testing/run_with_dummy_home.py b/testing/run_with_dummy_home.py
index 7bb6a12..5d0f20c 100755
--- a/testing/run_with_dummy_home.py
+++ b/testing/run_with_dummy_home.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright 2018 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.
@@ -10,8 +10,6 @@
 can contain config files that negatively affect test performance.
 """
 
-from __future__ import print_function
-
 import os
 import shutil
 import subprocess