Add missing git feature dep to preserve_executable_bit test (#12850)
## Summary
Without the `git` feature, it fails with:
```
error: Failed to initialize Git repository at `/home/mgorny/.local/share/uv/tests/.tmp01wGGK/temp/preserve_executable_bit`
stdout:
stderr: error: `git` operations are not allowed — are you missing a cfg for the `git` feature?
```
## Test Plan
cargo test --features python --profile=fast-build --no-default-features
