/usr/lib/x86_64-linux-gnu/libz.so is in zlib1g-dev 1:1.2.8.dfsg-2ubuntu4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /lib/x86_64-linux-gnu/libz.so.1.2.8
/lib/x86_64-linux-gnu/libz.so.1.2.8