follows #551338 to fix:
```python
=========================== short test summary info ============================
FAILED test_jrl_release.py::test_discover_package_roots_respects_gitignore - FileNotFoundError: [Errno 2] No such file or directory: 'git'
FAILED test_jrl_release.py::test_discover_package_roots_skips_submodules - FileNotFoundError: [Errno 2] No such file or directory: 'git'
FAILED test_jrl_release.py::test_git_submodule_dirs_empty_without_gitmodules - FileNotFoundError: [Errno 2] No such file or directory: 'git'
======================== 3 failed, 112 passed in 1.02s =========================
```
