gradle: setup hook respects java override

Before this commit, an expression like `pkgs.gradle_8.override { java = pkgs.openjdk17; }` would produce a
gradle package which uses jdk 17, but has a setup hook which uses jdk 21.

pkgs/development/tools/build-managers/gradle/default.nix

@@ -307,7 +307,7 @@ let
               '';
         };
       };
-      passthru.jdk = defaultJava;
+      passthru.jdk = java;
       passthru.wrapped = callPackage wrapGradle {
         gradle-unwrapped = mkGradle genArgs;
       };