Fix Gradle warning in RuntimeHintsAgentPlugin

Fixing the following warning in the runtime hints plugin configuration:
https://docs.gradle.org/8.9/userguide/upgrading_version_8.html#test_task_default_classpath

buildSrc/src/main/java/org/springframework/build/hint/RuntimeHintsAgentPlugin.java

@@ -26,7 +26,9 @@ import org.gradle.api.attributes.LibraryElements;
 import org.gradle.api.attributes.Usage;
 import org.gradle.api.attributes.java.TargetJvmVersion;
 import org.gradle.api.plugins.JavaPlugin;
+import org.gradle.api.plugins.jvm.JvmTestSuite;
 import org.gradle.api.tasks.testing.Test;
+import org.gradle.testing.base.TestingExtension;
 
 import java.util.Collections;
 
@@ -47,6 +49,8 @@ public class RuntimeHintsAgentPlugin implements Plugin<Project> {
 	public void apply(Project project) {
 
 		project.getPlugins().withType(JavaPlugin.class, javaPlugin -> {
+			TestingExtension testing = project.getExtensions().getByType(TestingExtension.class);
+			JvmTestSuite jvmTestSuite = (JvmTestSuite) testing.getSuites().getByName("test");
 			RuntimeHintsAgentExtension agentExtension = createRuntimeHintsAgentExtension(project);
 			Test agentTest = project.getTasks().create(RUNTIMEHINTS_TEST_TASK, Test.class, test -> {
 				test.useJUnitPlatform(options -> {
@@ -55,6 +59,8 @@ public class RuntimeHintsAgentPlugin implements Plugin<Project> {
 				test.include("**/*Tests.class", "**/*Test.class");
 				test.systemProperty("java.awt.headless", "true");
 				test.systemProperty("org.graalvm.nativeimage.imagecode", "runtime");
+				test.setTestClassesDirs(jvmTestSuite.getSources().getOutput().getClassesDirs());
+				test.setClasspath(jvmTestSuite.getSources().getRuntimeClasspath());
 				test.getJvmArgumentProviders().add(createRuntimeHintsAgentArgumentProvider(project, agentExtension));
 			});
 			project.getTasks().getByName("check", task -> task.dependsOn(agentTest));