GIT_WORK_TREE is invalid in colocated Git repo on jj 0.28.2

[ony]

Description

My post-rewrite Git hook started to fail when executing something like git --work-tree="$PWD" commit --amend within root of work-tree.

Issue manifests on 0.28.2. But on 0.26.0 everything works fine.

Steps to Reproduce the Problem

In some empty folder

1. jj git init --colocate
2. GIT_WORK_TREE="$PWD" jj show --no-pager @-

Expected Behavior

GIT_WORK_TREE="$PWD" should not affect jj as long as PWD matches repository root. E.g.

Commit ID: 0000000000000000000000000000000000000000
Change ID: zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
Author   : (no name set) <(no email set)> (1970-01-01 02:00:00)
Committer: (no name set) <(no email set)> (1970-01-01 02:00:00)

    (no description set)

Actual Behavior

Internal error: The repository appears broken or inaccessible
Caused by:
1: Failed to open git repository
2: Failed to load the git configuration
3: The key "core.worktree" (possibly from GIT_WORK_TREE) was invalid

Without GIT_WORK_TREE="$PWD" there is no issue.

Specifications

• Platform: NixOS 24.11 (with jj from master)
• Version: 0.28.2