Git commands called from Lefthook use incorrect working directory in Git worktree

[praseodym]

🔧 Summary

Git commands called from Lefthook use incorrect working directory in Git worktree

Lefthook version

1.12.1

Steps to reproduce

1. Create a new Git repository with an empty directory subdir in it
2. Configure Lefthook using

assert_lefthook_installed: true

pre-commit:
  commands:
    date:
      root: "subdir/"
      run: >
        pwd &&
        date > test.txt &&
        git add -v test.txt

3. touch subdir/a; git add subdir
4. Commit and observe that test.txt is created in subdir
5. Create a git worktree using git worktree add ../lefthook-test-worktree
6. cd ../lefthook-test-worktree; touch subdir/b; git add subdir
7. Commit this change

Expected results

The date in subdir/test.txt is updated

Actual results

A new file test.txt is created in the root of the repository. This is because GIT_DIR is set when running the git add command in the worktree, causing the file to be added in the wrong directory.