/usr/lib/syslog-ng/libsyslog-ng.so is in syslog-ng-dev 3.5.6-2.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/syslog-ng/libsyslog-ng-3.5.6.so
/usr/lib/syslog-ng/libsyslog-ng-3.5.6.so