oscommands: use a pty for stderr

[oliverpool]

• PR Description

Currently making remote operations with a secure-key-backed ssh key will shows the following output in the terminal:

notifiy_start: exec(/usr/lib/ssh/ssh-askpass): No such file or directory

With this PR, it will show:

Confirm user presence for key ...

• Please check if the PR fulfills these requirements

• Cheatsheets are up-to-date (run go run scripts/cheatsheet/main.go generate)
• Code has been formatted (see here)
• Tests have been added/updated (see here for the integration test guide)
• Text is internationalised (see here)
• Docs (specifically docs/Config.md) have been updated if necessary
• You've read through your own file changes for silly mistakes etc

[oliverpool]

This is my first PR for this project and first experience with PTYs (I had to dig quite a lot to understand the wrong Git output).

Let me know if this workaround makes sense and if my implementation looks sensible!

Thank you for starting and maintaining this great project!

[oliverpool]

Maybe this workaround should be disabled for windows?

---

I just realized that self.getCmdHandler a couple of lines below is also creating a pty. Maybe this function could support this usecase as well 🤔

[oliverpool]

I am in the process of switching to a tpm-backed ssh key: #4018

(Hence not much interested in finishing this)