python: explicitly require python3

Ubuntu has dropped the `python` symlink to `python2` [1] instead of
redirecting it to `python3` like other distros are doing, which means
that if we want to build Mesa on Ubuntu we need the `python3` shebang.

[1] https://lists.ubuntu.com/archives/ubuntu-devel/2020-January/040882.html

Reported-by: Vinson Lee <vlee@freedesktop.org>
Signed-off-by: Eric Engestrom <eric@engestrom.ch>
Acked-by: Jose Fonseca <jfonseca@vmware.com>
Reviewed-by: Alyssa Rosenzweig <alyssa@collabora.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3674>

bin/meson_get_version.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # encoding=utf-8
 # Copyright © 2017 Intel Corporation
 

bin/symbols-check.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 import argparse
 import os

src/egl/egl-entrypoint-check.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 import argparse
 from generate.eglFunctionList import EGL_FUNCTIONS as GLVND_ENTRYPOINTS

src/egl/generate/gen_egl_dispatch.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # (C) Copyright 2016, NVIDIA CORPORATION.
 # All Rights Reserved.

src/mapi/new/genCommon.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # (C) Copyright 2015, NVIDIA CORPORATION.
 # All Rights Reserved.

src/mapi/new/gen_gldispatch_mapi.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # Copyright (C) 2010 LunarG Inc.
 # (C) Copyright 2015, NVIDIA CORPORATION.