Fix Sidekiq JSON logging

The 'Listening on queues' message was logged before we set the log
format (if enabled) to JSON, so it would never be in JSON. We can just
move it to later to ensure that it uses the correct format.

config/initializers/sidekiq.rb

@@ -30,8 +30,6 @@ Sidekiq.configure_server do |config|
   config.options[:strict] = false
   config.options[:queues] = Gitlab::SidekiqConfig.expand_queues(config.options[:queues])
 
-  Sidekiq.logger.info "Listening on queues #{config.options[:queues].uniq.sort}"
-
   if enable_json_logs
     config.log_formatter = Gitlab::SidekiqLogging::JSONFormatter.new
     config.options[:job_logger] = Gitlab::SidekiqLogging::StructuredLogger
@@ -41,6 +39,8 @@ Sidekiq.configure_server do |config|
     config.error_handlers.reject! { |handler| handler.is_a?(Sidekiq::ExceptionHandler::Logger) }
   end
 
+  Sidekiq.logger.info "Listening on queues #{config.options[:queues].uniq.sort}"
+
   config.redis = queues_config_hash
 
   config.server_middleware(&Gitlab::SidekiqMiddleware.server_configurator(