Replace ActiveSupport::Logger with DiscourseLogstashLogger when enabled.

config/initializers/100-lograge.rb

@@ -96,6 +96,11 @@ if (Rails.env.production? && SiteSetting.logging_provider == 'lograge') || ENV["
       config.lograge.logger = DiscourseLogstashLogger.logger(
         uri: ENV['LOGSTASH_URI'], type: :rails
       )
+
+      # Remove ActiveSupport::Logger from the chain and replace with Lograge's
+      # logger
+      Rails.logger.instance_variable_get(:@chained).pop
+      Rails.logger.chain(config.lograge.logger)
     end
   end
 end