How to push using ssh key?

**Describe the bug**
I use mostly ssh key to push and when using gitui to push it jusr error out with `git error:Couldn't find credentials `

**To Reproduce**
Steps to reproduce the behavior:
1. Install gitui with homebrew
2. Open gitui
3. Type p to push
4. See error

**Expected behavior**
It should just use the configured ssh key from ssh-agent

**Screenshots**
If applicable, add screenshots to help explain your problem.

**Context (please complete the following information):**
- macOS Montery 12.1
- GitUI Version 0.21.0

**Additional context**
Add any other context about the problem here.

Reproduce el fallo del push en macOS Monterey con GitUI 0.21.0, usando una clave SSH cargada en ssh-agent. Rastrea el manejo de credenciales del push de GitUI y verifica que una clave configurada de ssh-agent se use correctamente en lugar de producir "Couldn't find credentials".

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