Apache Airflow SFTP provider: Path traversal in SFTPHook.retrieve_directory

A path traversal in the SFTP provider (`SFTPHook.retrieve_directory` / `SFTPOperator(operation=get)`) let a malicious or compromised remote SFTP server write files outside the configured local destination directory via crafted directory-entry names. No Airflow account is required — the attack surface is any deployment downloading directories from an untrusted SFTP server. Upgrade `apache-airflow-providers-sftp` to 5.8.1 or later.