/etc/apache2/mods-available/auth_mellon.load is in libapache2-mod-auth-mellon 0.12.0-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | # Depends: authn_core
LoadModule auth_mellon_module /usr/lib/apache2/modules/mod_auth_mellon.so
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