ocamlPackages.conduit: use dune 3

pkgs/development/ocaml-modules/conduit/async.nix

···
     src
     ;
 
+  duneVersion = "3";
+
   buildInputs = [ ppx_sexp_conv ppx_here ];
 
   propagatedBuildInputs = [

pkgs/development/ocaml-modules/conduit/default.nix

···
   pname = "conduit";
   version = "6.1.0";
 
-  minimalOCamlVersion = "4.03";
+  minimalOCamlVersion = "4.08";
+  duneVersion = "3";
 
   src = fetchurl {
     url = "https://github.com/mirage/ocaml-conduit/releases/download/v${version}/conduit-${version}.tbz";

pkgs/development/ocaml-modules/conduit/lwt-unix.nix

···
 buildDunePackage {
   pname = "conduit-lwt-unix";
   inherit (conduit-lwt) version src;
+  duneVersion = "3";
 
   buildInputs = [ ppx_sexp_conv ];
 

pkgs/development/ocaml-modules/conduit/lwt.nix

···
 buildDunePackage {
   pname = "conduit-lwt";
   inherit (conduit) version src;
+  duneVersion = "3";
 
   buildInputs = [ ppx_sexp_conv ];
 

pkgs/development/ocaml-modules/conduit/mirage.nix

···
   pname = "conduit-mirage";
 
   inherit (conduit-lwt) version src;
+  duneVersion = "3";
 
   nativeBuildInputs = [ ppx_sexp_conv ];