/usr/lib/mono/4.5/RabbitMQ.Client.dll is in libmono-rabbitmq4.0-cil 4.6.2.7+dfsg-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/mono/4.5/../gac/RabbitMQ.Client/4.0.0.0__b03f5f7f11d50a3a/RabbitMQ.Client.dll