ssh-agent on bash

**Expected behaviour**

when ssh agent is used, one of the keys added to the ssh agent is used

**Current behaviour**

when ssh agent is used, `~/.ssh/id_rsa` is used instead of one the keys added to the agent

**To Reproduce**
```
eval (ssh-agent -s)
ssh-add /Users/andrea/.ssh/key_other_than_id_rsa
k3sup install --host=192.168.0.5 --user=andrea
Running: k3sup install
2025/02/20 21:26:31 192.168.0.5
Public IP: 192.168.0.5
Error: unable to load the ssh key with path "/Users/andrea/.ssh/id_rsa": unable to read file: /Users/andrea/.ssh/id_rsa, open /Users/andrea/.ssh/id_rsa: no such file or directory
```

**Screenshots / console output**

See above

**Versions:**
- OS: macOS 15.3.1 (24D70)
- K3sup Version: Version: 0.13.6
Git Commit: 752c22af38d11b9d57f7a5ae4add3571d0d57b3a
- Bash version: GNU bash, version 3.2.57(1)-release (arm64-apple-darwin24)

**Additional context**

looking at the repo on how the ssh-agent setup works, this should be supported and working on bash, what do I miss? :)