[ bug ] Error: private key is encrypted

Describe the bug gitui can't deal with encrypted private keys.

To Reproduce Steps to reproduce the behavior:

1. Create an encrypted key
2. add the key to your ~/.gitconfig under user.signingkey
3. Attempt to commit files using gitu

Expected behavior Use the ssh-agent or ask for the password.

Context (please complete the following information):

• OS/Distro + Version: ubuntu 24]
• GitUI Version: gitui 0.26.3 2024-06-02 (95e1d4d)
• Rust version: 1.81.0