git-credential: disable prompt when not attached to a tty

[pmrowla]

Fixes #234

[codecov-commenter]

Codecov Report

Patch coverage: 45.45% and project coverage change: -0.12 ⚠️

Comparison is base (885a03d) 81.34% compared to head (03568af) 81.23%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #235      +/-   ##
==========================================
- Coverage   81.34%   81.23%   -0.12%     
==========================================
  Files          27       27              
  Lines        4005     4012       +7     
  Branches      706      708       +2     
==========================================
+ Hits         3258     3259       +1     
- Misses        624      630       +6     
  Partials      123      123              

Impacted Files	Coverage Δ
src/scmrepo/git/credentials.py	59.58% <45.45%> (-0.97%)	⬇️

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