Upgrading the control plane operating system fails due to ssh authentication failure during FFU from 16.2 to 17.1

Issue

• During the FFU from 16.2 to 17.1, sh /home/stack/overcloud_upgrade_prepare.shin Chapter 10. Upgrading the control plane operating system fails due to ssh authentication failure with the below messages.

> 2024-02-14 13:19:59.336660 | 005056bf-6bcd-859a-358e-000000000034 |      FATAL | Wait for connection to become available | 192.168.24.27 | error={"changed": > false, "elapsed": 2403, "msg": "timed out waiting for ping module test: Data could not be sent to remote host \"192.168.24.27\". Make sure this host can be > reached over ssh: load pubkey \"/home/stack/overcloud-deploy/overcloud/ssh_private_key\": Invalid key length\r\nWarning: Permanently added '192.168.24.27' 
> (ED25519) to the list of known hosts.\r\ntripleo-admin@192.168.24.27: Permission denied (publickey,password).\r\n"}

• SSH manually from director to Overcloud nodes with tripleo-admin user success, but SSH during the sh /home/stack/overcloud_upgrade_prepare.sh fails.