/usr/lib/x86_64-linux-gnu/libgavl.so is in libgavl-dev 1.2.0-4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libgavl.so.1.0.0
/usr/lib/x86_64-linux-gnu/libgavl.so.1.0.0