feat(shorebird_cli): add forEachRef to Git

[felangel]

Description

• feat(shorebird_cli): add forEachRef to Git (part of feat: shorebird should support switching flutter versions #1037)

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (fb5bcac) 100.00% compared to head (b296d86) 100.00%.

❗ Current head b296d86 differs from pull request most recent head b74a6f9. Consider uploading reports for the commit b74a6f9 to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1062   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           84        84           
  Lines         3165      3173    +8     
=========================================
+ Hits          3165      3173    +8     

Files Changed	Coverage Δ
packages/shorebird_cli/lib/src/git.dart	100.00% <100.00%> (ø)

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