Use Signed-By for apt instead of trusted.gpg.d

Please transition to using Signed-By instead of installing gpg key in /etc/apt/trusted.gpg.d.

Move /etc/apt/trusted.gpg.d/zabbix-official-repo.gpg to /usr/share/keyrings/zabbix-official-repo.gpg

Change /etc/apt/sources.list.d/zabbix.list from

deb https://repo.zabbix.com/zabbix/6.0/debian bullseye main
deb-src https://repo.zabbix.com/zabbix/6.0/debian bullseye main

to

deb [signed-by=/usr/share/keyrings/zabbix-official-repo.gpg] http://repo.zabbix.com/zabbix/6.0/debian bullseye main
deb [signed-by=/usr/share/keyrings/zabbix-official-repo.gpg] http://repo.zabbix.com/zabbix-agent2-plugins/1/debian bullseye main

Debian's documentation for this is available here: https://wiki.debian.org/DebianRepository/UseThirdParty

A writeup on why this should be done is available here: https://blog.cloudflare.com/dont-use-apt-key/