fix: use enqueued_at for enqueued_at

broken with #1444

Author: smoke

instrumentation/sidekiq/lib/opentelemetry/instrumentation/sidekiq/middlewares/server/tracer_middleware.rb

@@ -32,7 +32,7 @@ def call(_worker, msg, _queue)
 
               extracted_context = OpenTelemetry.propagation.extract(msg)
               created_at = time_from_timestamp(msg['created_at'])
-              enqueued_at = time_from_timestamp(msg['created_at'])
+              enqueued_at = time_from_timestamp(msg['enqueued_at'])
               scheduled_at = time_from_timestamp(msg['at']) unless msg['at'].nil?
               OpenTelemetry::Context.with_current(extracted_context) do
                 if instrumentation_config[:propagation_style] == :child