Update config path for submit_md_using_config.py

[MM0hsin]

Currently submit_md_using_config.py sets the directory with ../../..:

config = JanusConfigfile(
    Path("../../../tests/calculations/configs/config_janus_md.yml").resolve()
)

So running this with verdi run... may cause issues. So ideally it should be relative to the aiida_mlip file as in submit__using_config.py:

# __file__ changes depending on where verdi run is called
DATA_PATH = Path(aiida_mlip.__file__).parent.parent / "tests" / "calculations"