fix: lower minimum required git version

[bryanoltman]

Description

CodeMagic users have reported that the minimum git version we set is too high. This change lowers it to what we've seen CodeMagic machines report.

Fixes https://github.com/shorebirdtech/shorebird/issues/893

Type of Change

• [ ] ✨ New feature (non-breaking change which adds functionality)
• [x] 🛠️ 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