/etc/apt/apt.conf.d/20listchanges is in apt-listchanges 2.85.8ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | DPkg::Pre-Install-Pkgs { "/usr/bin/apt-listchanges --apt || test $? -ne 10"; };
DPkg::Tools::Options::/usr/bin/apt-listchanges::Version "2";
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