acceptance/helpers.rb: add signed-by to apt sources.list

acceptance/helpers.rb

@@ -235,6 +235,15 @@ def set_up_initial_agent_on(host, initial_package_version_or_collection)
                                   end
 
           install_puppet_agent_on(host, agent_install_options)
+
+          # beaker-puppet doesn't add signing information to the apt source list, but this module does.
+          # This discrepancy causes apt to error, so we manually add signing info.
+          if %r{debian|ubuntu}.match?(host['platform'])
+            step '(Agent) Add apt signing information' do
+              on(host, "sed -e 's/^deb http/deb [signed-by=\\/etc\\/apt\\/keyrings\\/GPG-KEY-puppet-20250406.asc] http/' /etc/apt/sources.list.d/puppet*.list -i")
+            end
+          end
+
           teardowns << -> do
             remove_installed_agent(host)
           end