Debian installation instructions still use `/etc/apt/trusted.gpg.d` for storing the key

This violates https://wiki.debian.org/DebianRepository/UseThirdParty, which states:

> ... The certificate MUST NOT be placed in /etc/apt/trusted.gpg.d or loaded by apt-key add.
>
>If future updates to the certificate will be managed by an apt/dpkg package as recommended below, then it SHOULD be downloaded into /usr/share/keyrings using the same filename that will be provided by the package. If it will be managed locally , it SHOULD be downloaded into /etc/apt/keyrings instead.

Please update the instructions accordingly.

Maybe also take into account that Debian 13 and Ubuntu 24.04 will default to the s.c. "deb822" style `*.sources` files in favor of the old `*.list` files in `/etc/apt/sources.list.d`. See `man 5 sources.list` for the details.

Locate the Debian installation instructions and review the current /etc/apt/trusted.gpg.d and apt-key guidance against DebianRepository/UseThirdParty. Also read man 5 sources.list for the *.sources and *.list formats; done means the instructions use the recommended keyring location and account for Debian 13 and Ubuntu 24.04.

Written by the indexing model from the issue text.