[python] Remove use of generic python shebang, update CI

Fixes #10465

Following discussion we don't allow a generic `/usr/bin/python`
shebang anymore. We thus move all the scripts [but one] to python3,
and add python3 to the Azure base environment.

Unfortunately we still depend on python2 for the update-compat.py
script, see #10491

We thus have to complement #10467 adding python2 back to Nix,
until #10491 is fixed.

1 files changed, 1 insertions, 1 deletions

diff --git a/dev/tools/update-compat.py b/dev/tools/update-compat.py
index 0338cd42c7..c7bb36b6d3 100755
--- a/dev/tools/update-compat.py
+++ b/dev/tools/update-compat.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python2
 from __future__ import with_statement
 import os, re, sys, subprocess