emacs: use relative downloaded paths in update-from-overlay.py

            name,

            sha,

            emacs_overlay=emacs_overlay,

            here_directory=here_directory,

            logger=logger,

        )

    name: str,

    sha: str,

    emacs_overlay: EmacsOverlay,

    here_directory: HereDirectory,

    logger: logging.Logger,

) -> None:

    """Fetch a fileset from emacs overlay.

    basename = emacs_overlay.elisp_packages_set[name]["basename"]

    url = f"{emacs_overlay.raw_url}/{sha}/{location}/{basename}"

    destination = here_directory.path / basename

    logger.debug(f"Getting {url}")

    with (

        urllib.request.urlopen(url) as input_stream,

        open(destination, "wb") as output_file,

        open(basename, "wb") as output_file,

    ):

        logger.info(f"Installing {destination}")

        logger.info(f"Installing {basename}")

        shutil.copyfileobj(input_stream, output_file)

    logger.debug("END")