tools: fix shebang to use python3 by default

PR-URL: #44531
Reviewed-By: Feng Yu <F3n67u@outlook.com>
Reviewed-By: Christian Clauss <cclauss@me.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Minwoo Jung <nodecorelab@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>

tools/test.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # Copyright 2008 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without