logs: info not warn for docker registry 5xx

lib/datasource/docker/index.js

@@ -173,7 +173,7 @@ async function getManifestResponse(registry, repository, tag) {
       throw new Error('registry-failure');
     }
     if (err.statusCode >= 500 && err.statusCode < 600) {
-      logger.warn(
+      logger.info(
         {
           err,
           registry,