/usr/lib/mono/compat-2.0/ICSharpCode.SharpZipLib.dll is in libmono-sharpzip2.6-cil 3.2.8+dfsg-4ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/mono/compat-2.0/../gac/ICSharpCode.SharpZipLib/2.6.0.0__1b03e6acf1164f73/ICSharpCode.SharpZipLib.dll