Fetch with `ssh` works, but pull does not.

**Describe the bug**

Fetch works... pull doesn't.

**To Reproduce**
Steps to reproduce the behavior:
1. `shift+f` -> fetch remote, yubikey touch for SSH, works fine :ok_hand:
2. `p` -> pull remote, yubikey touch for SSH, `fetch failed: git error: Bad credentials.` :sob:

**Context (please complete the following information):**
- OS/Distro + Version: Pop!_OS
- GitUI Version: #2157 branch
- Rust version: 1.77.0

**Additional context**

I have multiple ssh and gpg configs that occasionally will error on one that is incorrect, but then try another that is for `git` - I have not tried to see if that is the issue here, but I do not think it's at play in testing so far.

まず、報告された環境で SSH および YubiKey 認証を使い、`shift+f` の fetch パスと `p` の pull パスの違いを再現します。2 つの操作の認証動作を比較し、pull が `Bad credentials` なしで完了することを確認して fix を検証します。

索引モデルが issue の本文から書いたものです。