refactor(github): don’t warn deleting protected branch

lib/platform/github/storage.js

@@ -151,6 +151,8 @@ class Storage {
             { branch: branchName },
             'Branch to delete does not exist'
           );
+        } else if (err.message.startsWith('Cannot delete protected branch')) {
+          logger.info({ branch: branchName }, 'Cannot delete protected branch');
         } else {
           logger.warn({ err, branch: branchName }, 'Error deleting branch');
         }