Add Rails 8.0 to accepted framework versions

Previously, a log message stating "Detected untested Rails version 8.*"
would be emitted. This is incorrect, as we are now testing the agent
against Rails 8.0

lib/new_relic/agent/configuration/default_source.rb

@@ -139,7 +139,7 @@ def self.framework
               case Rails::VERSION::MAJOR
               when 3
                 :rails3
-              when 4..7
+              when 4..8
                 :rails_notifications
               else
                 ::NewRelic::Agent.logger.warn("Detected untested Rails version #{Rails::VERSION::STRING}")