Update SSH.NET dependency on SFTP tasks

The current SFTP tasks use SSH.NET 2024.1.0, which has a somewhat limited support for encryption algorithms in public key authentication (https://github.com/sshnet/SSH.NET/tree/2024.1.0?tab=readme-ov-file#public-key-authentication). Although it seems that the library supports more algorithms than the documentation suggests, SSH.NET 2025.0.0 should at least officially provide better support (https://github.com/sshnet/SSH.NET?tab=readme-ov-file#public-key-authentication). If the dependency was updated to 2025.0.0, we could promise support for a wider range of algorithms instead of either hoping that the target system accepts one of the algorithms 2024.1.0 officially supports, or hoping that the documentation of 2024.1.0 is inaccurate and an supposedly unsupported algorithm works.