another attempt at working around persistent channel src issue

artiq/channel.nix

@@ -0,0 +1,6 @@
+{ pkgs ? import <nixpkgs> {}, constituents}:
+pkgs.releaseTools.channel {
+  name = "main";
+  src = ./.;
+  inherit constituents;
+}

main.nix

@@ -38,9 +38,8 @@ let
   } // boardJobs // artiqPkgs;
 in
   jobs // {
-    channel = pkgs.releaseTools.channel {
-      name = "main";
-      src = "${generatedNix}";
+    channel = import "${generatedNix}/channel.nix" {
+      inherit pkgs;
       constituents = builtins.attrValues jobs;
     };
   }