repo.pp: use apt::keyring on distros where using keys stored in legacy trusted.gpg keyring (/etc/apt/trusted.gpg) is deprecated

[spicyprogramming]

Pull Request (PR) description

Newer apt based distros have deprecated apt keys stored in /etc/apt/trusted.gpg: installing zabbix agent with this module will result in the following warning:

root@ubuntu:~# apt update
Hit:1 http://archive.ubuntu.com/ubuntu jammy InRelease
Hit:2 http://security.ubuntu.com/ubuntu jammy-security InRelease    
Hit:3 http://archive.ubuntu.com/ubuntu jammy-updates InRelease      
Hit:4 http://apt.puppet.com jammy InRelease                         
Hit:5 http://repo.zabbix.com/zabbix/6.0/ubuntu jammy InRelease
Hit:6 http://archive.ubuntu.com/ubuntu jammy-backports InRelease
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
51 packages can be upgraded. Run 'apt list --upgradable' to see them.
W: http://repo.zabbix.com/zabbix/6.0/ubuntu/dists/jammy/InRelease: Key is stored in legacy trusted.gpg keyring (/etc/apt/trusted.gpg), see the DEPRECATION section in apt-key(8) for details.
root@ubuntu:~# 
root@ubuntu:~# lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 22.04 LTS
Release:	22.04
Codename:	jammy
root@ubuntu:~# 

AFAIK this started happening in Debian >= 12 and Ubuntu >= 22.04

Using apt::keyring instead of apt::key seems to silence the warning.

This Pull Request (PR) fixes the following issues

[bastelfreak]

This line looks rather odd and I doubt that it's required

[spicyprogramming]

That kind of hackish addition was just to keep the code under a reasonable number of characters per line but i guess after the changes to make the linter happy that ship has sailed anyway.