Bug: setup-git cannot find identity agent default if ssh was selected but not configured

[balupton]

If ssh was selected during gh auth login but no ssh keys exist, then setup-git will give a weird warning of:

/home/balupton/.local/share/dorothy/commands/ssh-helper: Unable to find the SSH_IDENTITY_AGENT of [default].

Full log, running on Ubuntu 24.04 WSL.

┌  Setup Git  ┐
┌  Install Git  ┐
The [git] utility is already installed. ✅
The [GnuPG] utility is already installed. ✅
The [OpenSSH Server] utility is already installed. ✅
Synchronizing state of ssh.service with SysV service script with /lib/systemd/systemd-sysv-install.
Executing: /lib/systemd/systemd-sysv-install enable ssh
The [delta] utility is already installed. ✅
The [diff] utility is already installed. ✅
The [Git Large File Storage] utility is already installed. ✅
The [Pinentry] utility is already installed. ✅
The [ssh-askpass] utility is already installed. ✅
The [gitell] utility is already installed. ✅
└  Install Git  ┘
Git Configuration: General
Git Configuration: Profile
Git Configuration: Auth
Git Configuration: Merge/Diff Tool: delta
Git Configuration: Editor: code -w --reuse-window
Git Configuration: Linux Credentials
Git Configuration: Signing
Git Configuration: Signing:
Signing was desired, however the key does not exist: /home/balupton/.ssh/balupton-2024
Run setup-git --configure to configure.
Git Configuration: Signing: Disabled
Git Configuration: Permissions
/home/balupton/.local/share/dorothy/commands/ssh-helper: Unable to find the SSH_IDENTITY_AGENT of [default].
Disabling for now...
SSH Configuration: .ssh/config
Updated configuration file: /home/balupton/.ssh/config
Add GitHub Keys to Known Hosts
# Host github.com found: line 1
# Host github.com found: line 2
# Host github.com found: line 3
/home/balupton/.ssh/known_hosts updated.
Original contents retained as /home/balupton/.ssh/known_hosts.old
The [GitHub CLI] utility is already installed. ✅
Git Configuration: Protocol: https
└  Setup Git  ┘