miku: Replace packageOverrides with an overlay

hosts/miku.nix

@@ -1,7 +1,6 @@
 { config, pkgs, modulesPath, lib, fetchGit, ... }:
 
 let
-  unstable = (import ../modules/unstable.nix config);
   customPkgs = import ../packages/overlay.nix;
 in {
   imports = [
@@ -79,15 +78,16 @@ in {
         propagatedBuildInputs = old.propagatedBuildInputs ++ [ prev.gsound ];
       });
     })
+
+    # Unstable, NUR, ...
+    (final: prev: {
+      unstable = (import ../modules/unstable.nix config);
+      nur = (import ../modules/nur.nix pkgs);
+    })
     
     customPkgs
   ];
 
-  nixpkgs.config.packageOverrides = pkgs: {
-    unstable = unstable;
-    nur = (import ../modules/nur.nix pkgs);
-  };
-
   security = {
     pam.loginLimits = [
       {
@@ -259,7 +259,7 @@ in {
     enable = true;
     qemuOvmf = true;
     #qemuRunAsRoot = false;
-    qemuPackage = unstable.qemu;
+    qemuPackage = pkgs.unstable.qemu;
     qemuVerbatimConfig = ''
       seccomp_sandbox = 0
       cgroup_device_acl = [