nixpkgs-plugin-update: no token fallback (#471396)

    @retry(urllib.error.URLError, tries=4, delay=3, backoff=2)

    def get_latest_tag(self) -> str | None:

        try:

            if not self.token or self.token == "":

                log.info(

                    "No GitHub token available for %s/%s, using git ls-remote fallback",

                    self.owner,

                    self.repo,

                )

                return super().get_latest_tag()

            # FIXME: This fetches all tags. We need to find a way to check if a tag exists in

            # an ancestor of the default branch.

            query = """