fix: write portable TOML paths in config tests

- use POSIX path strings for generated TOML in git_dir/work_tree tests

- avoid Windows backslash escape parsing failures under tomllib

Author: Kingson4Wu

tests/test_config.py

@@ -210,9 +210,9 @@ def test_git_dir_work_tree_requires_allowlist_policy(tmp_path):
                 tmp_path,
                 f"""
 [[repos]]
-path = "{work}"
-git_dir = "{git_dir}"
-work_tree = "{work}"
+path = "{work.as_posix()}"
+git_dir = "{git_dir.as_posix()}"
+work_tree = "{work.as_posix()}"
 """,
             )
         )