bump copyright
Distinguish between Xfce and os-cillation copyrights in help text (like it is done in doc and configure.ac)
Looks like this now:
$./exo-desktop-item-edit/exo-desktop-item-edit -V
exo-desktop-item-edit 4.19.0git-2c5648c6
Copyright (c) 2005-2007
os-cillation e.K. All rights reserved.
Copyright (c) 2008-2024
The Xfce development team. All rights reserved.
Written by Benedikt Meurer <benny@xfce.org>.
exo-desktop-item-edit comes with ABSOLUTELY NO WARRANTY,
You may redistribute copies of exo-desktop-item-edit under the terms of
the GNU Lesser General Public License which can be found in the
exo source package.
Please report bugs to <https://gitlab.xfce.org/xfce/exo>.