Add Arch Linux support

Arch Linux has a rolling release so it ignores the actual releases. It
also only supports the latest Puppet version so it doesn't make sense to
look at the actually supported Puppet versions.

lib/puppet_metadata/beaker.rb

@@ -65,7 +65,7 @@ def os_release_to_setfile(os, release, use_fqdn: false, pidfile_workaround: fals
       # Return whether a Beaker setfile can be generated for the given OS
       # @param [String] os The operating system
       def os_supported?(os)
-        ['CentOS', 'Fedora', 'Debian', 'Ubuntu'].include?(os)
+        ['Archlinux', 'CentOS', 'Fedora', 'Debian', 'Ubuntu'].include?(os)
       end
 
       private

lib/puppet_metadata/github_actions.rb

@@ -56,10 +56,15 @@ def beaker_os_releases
       majors = puppet_major_versions
 
       metadata.operatingsystems do |os, releases|
-        releases&.each do |release|
-          majors.each do |puppet_version|
-            if AIO.has_aio_build?(os, release, puppet_version[:value])
-              yield [os, release, puppet_version]
+        case os
+        when 'Archlinux', 'Gentoo'
+          yield [os, 'rolling', metadata.puppet_major_versions.max]
+        else
+          releases&.each do |release|
+            majors.each do |puppet_version|
+              if AIO.has_aio_build?(os, release, puppet_version[:value])
+                yield [os, release, puppet_version]
+              end
             end
           end
         end