installShellFiles: set passthru directly instead of overriding it

pkgs/by-name/in/installShellFiles/package.nix

···
 }:
 
 # See the header comment in ./setup-hook.sh for example usage.
-let
-  setupHook = makeSetupHook { name = "install-shell-files"; } ./setup-hook.sh;
-in
-setupHook.overrideAttrs (oldAttrs: {
-  passthru = (oldAttrs.passthru or { }) // {
+makeSetupHook {
+  name = "install-shell-files";
+  passthru = {
     tests = lib.packagesFromDirectoryRecursive {
       inherit callPackage;
       directory = ./tests;
     };
   };
-})
+} ./setup-hook.sh