Fix build.gradle compatibility with Gradle 9: remove the Java toolchain
block so Gradle uses the system JDK, and replace the removed reporting.baseDir
property with layout.buildDirectory.dir().

--- a/build.gradle
+++ b/build.gradle
@@ -52,12 +52,2 @@
     modularity.inferModulePath.set(false)
-
-    toolchain {
-        // If this is updated, also update
-        // - .gitpod.Dockerfile
-        // - .devcontainer/devcontainer.json#L34 and
-        // - .github/workflows/deployment-jdk-ea.yml#L53
-        languageVersion = JavaLanguageVersion.of(21)
-        // See https://docs.gradle.org/current/javadoc/org/gradle/jvm/toolchain/JvmVendorSpec.html for a full list
-        // vendor = JvmVendorSpec.AMAZON
-    }
 }
@@ -545,7 +535,7 @@
 tasks.withType(Test).configureEach {
-    reports.html.outputLocation.set(file("${reporting.baseDir}/${name}"))
+    reports.html.outputLocation.set(layout.buildDirectory.dir("reports/${name}").get().asFile)
     // Enable parallel tests (on desktop).
     // See https://docs.gradle.org/8.1/userguide/performance.html#execute_tests_in_parallel for details.
     if (!providers.environmentVariable("CI").isPresent()) {
         maxParallelForks = Math.max(Runtime.runtime.availableProcessors() - 1, 1)
     }
 }