Repair warning message when worker does not end promptly (#4637)

Co-authored-by: Oleg Pudeyev <[email protected]>

Author: p-datadog

lib/datadog/core/workers/async.rb

@@ -53,7 +53,7 @@ def terminate
                 worker.join
               end
             rescue Timeout::Error
-              Datadog.logger.debug { "Worker thread did not end after 0.5 seconds: #{self}" }
+              Datadog.logger.debug { "Worker thread did not end after #{SHUTDOWN_TIMEOUT} seconds: #{self}" }
             end
             true
           end