refactor: downgrade docker warn to info

lib/datasource/docker.js

@@ -148,7 +148,7 @@ async function getTags(registry, name) {
       logger.debug({ err });
       return null;
     }
-    logger.warn({ err, name }, 'Error getting docker image tags');
+    logger.info({ err, name }, 'Warning: Error getting docker image tags');
     return null;
   }
 }