fix: actively handle 401 auth deny from docker registries

lib/datasource/docker.js

@@ -136,6 +136,19 @@ async function getTags(registry, name) {
     logger.trace({ tags });
     return tags;
   } catch (err) /* istanbul ignore next */ {
+    logger.debug(
+      {
+        err,
+        name,
+        message: err.message,
+        body: err.response ? err.response.body : undefined,
+      },
+      'docker.getTags() error'
+    );
+    if (err.statusCode === 401) {
+      logger.info('Not authorised to look up docker tags');
+      return null;
+    }
     if (err.statusCode >= 500 && err.statusCode < 600) {
       logger.warn({ err }, 'docker registry failure: internal error');
       throw new Error('registry-failure');
@@ -148,7 +161,7 @@ async function getTags(registry, name) {
       logger.debug({ err });
       return null;
     }
-    logger.info({ err, name }, 'Warning: Error getting docker image tags');
+    logger.warn('Error getting docker image tags');
     return null;
   }
 }