Additions to Modulesync 5.3.0 PR

[Rathios]

All tests are passing on my Fedora 36 box with these changes.

• Adds net-ftp as a dependency gem for testing on Fedora. Fresh Ruby 3.1 on Fedora does not include this gem, making tests related to apt_key fail. Not sure if this is a Fedora problem or a test suite problem.
• Fixes Zabbix Agent and Server tests concerning OSes that have since moved to systemd. These can't have worked in a long time.
• Temporarily disables Gentoo tests. Support for Gentoo is broken and I don't have the means to fix it. Gentoo is still in metadata.json. Users should have complained by now if it mattered. Whoever wants to fix it can fix the spec tests at the same time.

[ekohl]

Adds net-ftp as a dependency gem for testing on Fedora. Fresh Ruby 3.1 on Fedora does not include this gem, making tests related to apt_key fail. Not sure if this is a Fedora problem or a test suite problem.

Resolved in puppetlabs/puppetlabs-apt#1050.

So I only picked the 2 other commits.