langgraph*: use `tag` option to `fetchFromGitHub`

  src = fetchFromGitHub {

    owner = "langchain-ai";

    repo = "langgraph";

    rev = "refs/tags/checkpointduckdb==${version}";

    tag = "checkpointduckdb==${version}";

    hash = "sha256-wSrlFBfTcTgyE46uwv9GCyxRT1xVafgWyP2g87KUTAU=";

  };

  src = fetchFromGitHub {

    owner = "langchain-ai";

    repo = "langgraph";

    rev = "refs/tags/checkpointpostgres==${version}";

    tag = "checkpointpostgres==${version}";

    hash = "sha256-yHLkFUp+q/XOt9Y9Dog2Tgs/K2CU7Bfkkucdr9vAKSg=";

  };

  src = fetchFromGitHub {

    owner = "langchain-ai";

    repo = "langgraph";

    rev = "refs/tags/checkpointsqlite==${version}";

    tag = "checkpointsqlite==${version}";

    hash = "sha256-dh+cjcOp6rGFntz82VNfVyetcrQBdBFdXk5xFb0aR5c=";

  };

  src = fetchFromGitHub {

    owner = "langchain-ai";

    repo = "langgraph";

    rev = "refs/tags/checkpoint==${version}";

    tag = "checkpoint==${version}";

    hash = "sha256-obDK6wn+oo8zDQsidogwKTIgT5wuUH/l4y+12cttkd0=";

  };

  src = fetchFromGitHub {

    owner = "langchain-ai";

    repo = "langgraph";

    rev = "refs/tags/cli==${version}";

    tag = "cli==${version}";

    hash = "sha256-zTBeDJB1Xu/rWsvEC/L4BRzxyh04lPYV7HQNHoJcskk=";

  };