Prevent git from prompting for credentials

[perlpunk]

There can be situations where git needs credentials and prompts the user,

• Trying to push to via http
• Trying to push via ssh but without having a key, or a key with a passphrase
• Trying to fetch from a private repo via http or ssh

This does not make sense in automated code and results in a hanging process
waitign for input.

We can prevent a prompt by setting the following two variables:

https://git-scm.com/docs/git#Documentation/git.txt-codeGITASKPASScode

GIT_ASKPASS

If this environment variable is set, then Git commands which need to acquire
passwords or passphrases (e.g. for HTTP or IMAP authentication) will call this
program with a suitable prompt as command-line argument and read the password
from its STDOUT. See also the core.askPass option in git-config[1].

https://git-scm.com/docs/git#Documentation/git.txt-codeGITTERMINALPROMPTcode
GIT_TERMINAL_PROMPT

If this Boolean environment variable is set to false, git will not prompt on
the terminal (e.g., when asking for HTTP authentication).

This way we will immediately get an error message.

Issue: https://progress.opensuse.org/issues/174592

In this case the error presented to the user is:

"Unable to push Git commit
(/path/to/needles): remote: Support
for password authentication was removed on August 13, 2021. remote: Please see
https://docs.github.com/get-started/getting-started-with-git/about-remote-repositories#cloning-with-https-urls
for information on currently recommended modes of authentication. fatal:
Authentication failed for
'https://github.com/perlpunk/os-autoinst-needles-openQA/'"

That can be improved in a followup by adding a link to our documentation.

Note: That's for AC3 of the ticket

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.99%. Comparing base (b7aa773) to head (a42198e).
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6141   +/-   ##
=======================================
  Coverage   98.99%   98.99%           
=======================================
  Files         396      396           
  Lines       39637    39637           
=======================================
  Hits        39237    39237           
  Misses        400      400           

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