vyxal: update mill dependency to use fetchurl for version and URL locking

The source link for mill will be changing, so we need to specify the
download link for mill here.

Signed-off-by: Qiming Chu <[e-mail]>

pkgs/by-name/vy/vyxal/package.nix

···
   stdenvNoCC,
   clangStdenv,
   fetchFromGitHub,
+  fetchurl,
   mill,
   which,
 }:
···
 let
   # we need to lock the mill version, because an update will change the
   # fetched internal dependencies, thus breaking the deps FOD
-  lockedMill = mill.overrideAttrs (oldAttrs: {
+  lockedMill = mill.overrideAttrs (oldAttrs: rec {
     # should ideally match the version listed inside the `.mill-version` file of the source
     version = "0.11.12";
-    src = oldAttrs.src.overrideAttrs {
-      outputHash = "sha256-k4/oMHvtq5YXY8hRlX4gWN16ClfjXEAn6mRIoEBHNJo=";
+    src = fetchurl {
+      url = "https://github.com/com-lihaoyi/mill/releases/download/${version}/${version}-assembly";
+      hash = "sha256-k4/oMHvtq5YXY8hRlX4gWN16ClfjXEAn6mRIoEBHNJo=";
     };
   });
 in