doc: Update Peercoin copyright to 2024

Author: lateminer

COPYING

@@ -2,7 +2,7 @@ The MIT License (MIT)
 
 Copyright (c) 2009-2024 The Bitcoin Core developers
 Copyright (c) 2009-2024 Bitcoin Developers
-Copyright (c) 2011-2023 Peercoin developers
+Copyright (c) 2011-2024 Peercoin developers
 Copyright (c) 2013-2014 The NovaCoin developers
 Copyright (c) 2016-2023 The Qtum developers
 Copyright (c) 2014-2018 The Blackcoin developers