nixos/matrix-alertmanager: set NODE_ENV to production, fix shellcheck when it is enabled (#388000)

        MATRIX_ROOMS = concatenatedRooms;

        MATRIX_USER = cfg.matrixUser;

        MENTION_ROOM = if cfg.mention then "1" else "0";

        NODE_ENV = "production";

      };

      script = ''

        # shellcheck disable=SC2155

        export APP_ALERTMANAGER_SECRET=$(cat "''${CREDENTIALS_DIRECTORY}/secret")

        # shellcheck disable=SC2155

        export MATRIX_TOKEN=$(cat "''${CREDENTIALS_DIRECTORY}/token")

        exec ${lib.getExe cfg.package}

      '';