The package is named kaliko-archive-keyring, it’ll install the signing key in /usr/share/keyrings/deb.kaliko.me.gpg.

Then there are no changes to do in your source list as long as you previously followed recommendations to add deb.kaliko.me repositories.

The main advantage to use the package instead of manually add the key is that apt will notify the system when I release a new version of kaliko-archive-keyring shipping changes in my signing key (mainly key expiry date).
Then an apt update or whatever is used to maintain your system up to date will notify you a new version is available.

Install

In case you already have deb./kaliko.me repository setup just install the package:
apt install kaliko-archive-keyring

Otherwise, follow procedure on the dedicated page.