Replace arm64 for aarch64 in ::apt::source

[mpdude]

arm64 is a rather new player in the server market: AWS Gravitron instances use it, but it is also used when running Linux-based VMs on Apple's new M1 chips.

As someone explained on StackOverflow, the Linux Kernel uses aarch64 at the name for this architecture, and that's what is reported by Facter.

Apt, however, uses the arm64 architecture name for this platform.

This mismatch can cause bugs as in puppetlabs/docker, and thus my suggestion is to fix it here in a central location.

I am not familiar with Ruby programming and rspec-based acceptance tests. So, if that's a requirement for getting this merged, any help is greatly appreciated.

[CLAassistant]

All committers have signed the CLA.

[puppet-community-rangefinder]

apt::source is a type

that may have no external impact to Forge modules.

This module is declared in 233 of 578 indexed public Puppetfiles.

---

These results were generated with Rangefinder, a tool that helps predict the downstream impact of breaking changes to elements used in Puppet modules. You can run this on the command line to get a full report.

Exact matches are those that we can positively identify via namespace and the declaring modules' metadata. Non-namespaced items, such as Puppet 3.x functions, will always be reported as near matches only.