How to name files in /etc/apt/sources.list.d/ to be ignored without warnings?

cat >> /etc/apt/apt.conf.d/98ignore_extensions << \EOF
# Follow the pattern to add more extensions to ignore.
Dir::Ignore-Files-Silently:: "\.gz$";
Dir::Ignore-Files-Silently:: "\.save$";
Dir::Ignore-Files-Silently:: "\.distUpgrade$";
Dir::Ignore-Files-Silently:: "\.list_$";
EOF

I just move the files to ../sources.list.disabled/.

[kubuntu 18.04]

I could not work out why the suffixes .distUpgrade and .save were ignored when there did not appear to be anything that explicitly sets this.

Then I discovered apt-config dump | grep -i ignore has entries for these and others:

Dir::Ignore-Files-Silently "";
Dir::Ignore-Files-Silently:: "~$";
Dir::Ignore-Files-Silently:: "\.disabled$";
Dir::Ignore-Files-Silently:: "\.bak$";
Dir::Ignore-Files-Silently:: "\.dpkg-[a-z]+$";
Dir::Ignore-Files-Silently:: "\.ucf-[a-z]+$";
Dir::Ignore-Files-Silently:: "\.save$";
Dir::Ignore-Files-Silently:: "\.orig$";
Dir::Ignore-Files-Silently:: "\.distUpgrade$";

I just renamed my dodgy one to be of of those extensions. (I chose .orig)