/usr/share/lua/5.3/busted/compatibility.lua is in lua-busted 2.0~rc12-1-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/lua/5.3/busted/../../5.1/busted/compatibility.lua
/usr/share/lua/5.3/busted/../../5.1/busted/compatibility.lua