fix(rubygems): throw registry-failure when failing to download

lib/datasource/rubygems/get-rubygems-org.js

@@ -21,13 +21,13 @@ async function updateRubyGemsVersions() {
     logger.debug('Rubygems: Fetching rubygems.org versions');
     newLines = (await got(url, options)).body;
   } catch (err) /* istanbul ignore next */ {
-    if (err.statusCode === 416) {
-      logger.debug('Rubygems: No update');
-    } else {
+    if (err.statusCode !== 416) {
       logger.warn({ err }, 'Rubygems error - resetting cache');
       contentLength = 0;
       packageReleases = Object.create(null); // Because we might need a "constructor" key
+      throw new Error('registry-failure');
     }
+    logger.debug('Rubygems: No update');
     lastSync = new Date();
     return;
   }