builderv2: some git fetch errors can make builder's fetch action wait for interactive answer

[marmarek]

Qubes OS release

Qubes OS 4.3

Brief summary

When fetching non-existing repo from github over https, it responds with HTTP 401, for the client to authenticate (in case the repo actually exists, but is private). This results in interactive prompt from the dispvm doing fetch, with no timeout.
This is especially bad for build infra, which runs unattended.

Steps to reproduce

1. Change builder conf to fetch non-existing repo over https from github
2. Do qb package fetch

Expected behavior

The command should fail on fetching the repo

Actual behavior

Git prompts for login credentials interactively, with no timeout.

Additional information

Note, this may also happen in case of github outage, sometimes it fails this way.

Later error message suggests it might be about SSH_ASKPASS variable, it might be enough to either unset it or set to /bin/false.