nixos/zfs-replication: fix typo (#368764)

Author: GaetanLepage

nixos/modules/services/backup/zfs-replication.nix

@@ -92,7 +92,7 @@ in
             ++ (lib.optional cfg.followDelete "--follow-delete")
           );
         in
-        "${lib.getExe cfg.package} ${lib.concatStringSep " " args}";
+        "${lib.getExe cfg.package} ${lib.concatStringsSep " " args}";
       wantedBy = [
         "zfs-snapshot-daily.service"
         "zfs-snapshot-frequent.service"