Add go-git integration test

[pjbgf]

No description provided.

[Copilot]

Pull request overview

Adds a GitHub Actions workflow to run go-git’s test suite against the PR’s go-billy code, and updates the osfs BoundOS implementation/tests to correctly handle Windows drive-qualified absolute paths (needed for go-git + util helpers on Windows).

Changes:

• Add a new go-git-integration.yml workflow that checks out go-billy + go-git and runs go test ./... (and CLI tests when present) across Linux/macOS/Windows.
• Update BoundOS.absNoFollow / BoundOS.secureJoin to recognize and correctly join Windows drive-qualified absolute paths when the filesystem is rooted at the Windows host root.
• Add Windows-only tests for drive-qualified absolute paths and util.TempDir behavior on osfs.Default.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
osfs/os_bound.go	Adds Windows host-root drive path splitting and uses it in join/abs logic to support C:\... / UNC paths correctly.
osfs/os_bound_test.go	Adds Windows-only regression tests validating drive-qualified absolute paths and util.TempDir usage with osfs.Default.
.github/workflows/go-git-integration.yml	Introduces a go-git integration workflow that runs go-git (and CLI) tests against the local go-billy checkout on 3 OSes.

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