Remove get_ prefixes from Git helpers

[j178]

Follow-up to #2437.

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[codecov]

Codecov Report

❌ Patch coverage is 95.55556% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.55%. Comparing base (3ac4f9e) to head (27795be).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
crates/prek/src/git.rs	93.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2438      +/-   ##
==========================================
- Coverage   93.56%   93.55%   -0.02%     
==========================================
  Files         130      130              
  Lines       28050    28052       +2     
==========================================
- Hits        26245    26243       -2     
- Misses       1805     1809       +4     

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