[py3] Bump v8heapconstants.py and related files

Bug: v8:12581
Change-Id: I4d98e48801ffcfbe507c61ba296da67359e3f5cb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3568464
Auto-Submit: Alexander Schulze <alexschulze@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Liviu Rau <liviurau@chromium.org>
Commit-Queue: Alexander Schulze <alexschulze@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79743}

test/mkgrokdump/mkgrokdump.cc

@@ -19,6 +19,7 @@
 namespace v8 {
 
 static const char* kHeader =
+    "#!/usr/bin/env python3\n"
     "# Copyright 2019 the V8 project authors. All rights reserved.\n"
     "# Use of this source code is governed by a BSD-style license that can\n"
     "# be found in the LICENSE file.\n"

tools/debug_helper/gen-heap-constants.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright 2019 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.

tools/v8heapconst.py

+#!/usr/bin/env python3
 # Copyright 2019 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can
 # be found in the LICENSE file.