fix git related tests

[anmarchenko]

What does this PR do?
Fixes git tests that were too unstable to be usable.

Current version creates local origin for each test and then clones it (both as a shallow and full clone).

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 98.94737% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 99.05%. Comparing base (314ab7e) to head (5e89348).
Report is 1 commits behind head on main.

Files	Patch %	Lines
spec/datadog/ci/git/local_repository_spec.rb	98.94%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #162      +/-   ##
==========================================
+ Coverage   98.90%   99.05%   +0.15%     
==========================================
  Files         196      196              
  Lines        9326     9340      +14     
  Branches      404      404              
==========================================
+ Hits         9224     9252      +28     
+ Misses        102       88      -14     

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