Make WebGPU CTS scripts use Python3

Bug: None
Change-Id: I3286b7cef7473106c916f8d7c9bf3a3609dc44c6
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/86534
Reviewed-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
diff --git a/webgpu-cts/scripts/compile_src.py b/webgpu-cts/scripts/compile_src.py
index b08c0a7..91c0eb4 100755
--- a/webgpu-cts/scripts/compile_src.py
+++ b/webgpu-cts/scripts/compile_src.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # Copyright 2022 The Dawn Authors
 #