nixos/tsm-client: use `lib.concatLines`

nixos/modules/programs/tsm-client.nix

···
   inherit (lib.attrsets) attrNames filterAttrs hasAttr mapAttrs mapAttrsToList optionalAttrs;
   inherit (lib.modules) mkDefault mkIf;
   inherit (lib.options) literalExpression mkEnableOption mkOption;
-  inherit (lib.strings) concatStringsSep optionalString toLower;
+  inherit (lib.strings) concatLines optionalString toLower;
   inherit (lib.types) addCheck attrsOf lines nonEmptyStr nullOr package path port str strMatching submodule;
 
   # Checks if given list of strings contains unique
···
         mkLine = k: v: k + optionalString (v!="") "  ${v}";
         lines = mapAttrsToList mkLine attrset;
       in
-        concatStringsSep "\n" lines;
+        concatLines lines;
     config.stanza = ''
       server  ${config.name}
       ${config.text}
···
 
     ${optionalString (cfg.defaultServername!=null) "defaultserver  ${cfg.defaultServername}"}
 
-    ${concatStringsSep "\n" (mapAttrsToList (k: v: v.stanza) cfg.servers)}
+    ${concatLines (mapAttrsToList (k: v: v.stanza) cfg.servers)}
   '';
 
 in