repopick: Require python3

Change-Id: I95f598947a29b2095bd7539b1f279dccc1b25097
diff --git a/build/tools/repopick.py b/build/tools/repopick.py
index 7c83bc2..ef2df11 100755
--- a/build/tools/repopick.py
+++ b/build/tools/repopick.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # Copyright (C) 2013-2015 The CyanogenMod Project
 #           (C) 2017-2024 The LineageOS Project