Update copyright notices to 2023

debian/copyright

@@ -9,7 +9,7 @@ Files:
  debian/*
 Copyright:
  2003-2014 David Martínez Moreno <ender@debian.org>
- 2016 Christoph Biedl <debian.axhn@manchmal.in-ulm.de>
+ 2016-2023 Christoph Biedl <debian.axhn@manchmal.in-ulm.de>
 License: GPL-2.0-only
 
 License: GPL-2.0-only