patchPpdFilesHook: use getExe' in test

pkgs/by-name/pa/patchPpdFilesHook/test.nix

@@ -1,4 +1,5 @@
 {
+  lib,
   replaceVars,
   diffutils,
   stdenv,
@@ -6,6 +7,8 @@
 }:
 
 let
+  inherit (lib.meta) getExe';
+
   input = replaceVars ./test.ppd {
     keep = "cmp";
     patch = "cmp";
@@ -15,9 +18,9 @@ let
 
   output = replaceVars ./test.ppd {
     keep = "cmp";
-    patch = "${diffutils}/bin/cmp";
+    patch = getExe' diffutils "cmp";
     pathkeep = "/bin/cmp";
-    pathpatch = "${diffutils}/bin/cmp";
+    pathpatch = getExe' diffutils "cmp";
   };
 in