/usr/lib/x86_64-linux-gnu/libapt-inst.so is in libapt-pkg-dev 1.0.1ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libapt-inst.so.1.5.0
/usr/lib/x86_64-linux-gnu/libapt-inst.so.1.5.0