refactor: downgrade yarn.lock parsing error logs to info

lib/workers/package-file/index.js

@@ -70,7 +70,7 @@ async function renovatePackageFile(packageFileConfig) {
       }
       logger.trace({ yarnLockParsed });
     } catch (err) {
-      logger.warn({ yarnLock }, 'Could not parse yarn.lock');
+      logger.info({ yarnLock }, 'Warning: Exception parsing yarn.lock');
     }
   } else if (config.packageLock) {
     try {