/usr/lib/mono/4.0/ICSharpCode.SharpZipLib.dll is in libmono-sharpzip4.84-cil 2.10.8.1-1ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/mono/4.0/../gac/ICSharpCode.SharpZipLib/4.84.0.0__1b03e6acf1164f73/ICSharpCode.SharpZipLib.dll