git-hooks: Not all OSes ship Python 3 under "python"

macOS doesn't, for instance. Use a shell script to detect which python
to run, which is always available on all OSes due to how git is
packaged on Windows.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5060>

scripts/git-hooks/multi-pre-commit.hook

@@ -15,7 +15,7 @@
 # commit. They are executed in the order in which they are listed.
 ###########################################################
 
-HOOKS="scripts/git-hooks/pre-commit.hook scripts/git-hooks/pre-commit-python.hook"
+HOOKS="scripts/git-hooks/pre-commit.hook scripts/git-hooks/pre-commit-invoke-python.hook"
 
 # exit on error
 set -e

scripts/git-hooks/pre-commit-invoke-python.hook

@@ -0,0 +1,12 @@
+#!/bin/sh
+
+PYTHON="python3"
+if [[ $OS =~ Windows ]]; then
+  if type -p py &>/dev/null; then
+    PYTHON="py -3"
+  elif type -p python &>/dev/null; then
+    PYTHON="python"
+  fi
+fi
+
+$PYTHON "`dirname $0`/pre-commit-python.hook"

scripts/git-hooks/pre-commit-python.hook

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