pdftk: use minimal jre

pkgs/by-name/pd/pdftk/package.nix

···
   stdenv,
   fetchFromGitLab,
   gradle_8,
-  jre,
+  jre_headless,
+  jre_minimal,
   runtimeShell,
 }:
 let
   # "Deprecated Gradle features were used in this build, making it incompatible with Gradle 9.0."
   gradle = gradle_8;
+
+  jre = jre_minimal.override {
+    modules = [
+      "java.base"
+      "java.desktop"
+    ];
+    jdk = jre_headless;
+  };
 in
 stdenv.mkDerivation rec {
   pname = "pdftk";