LUCENE-9448, LUCENE-9990: fix Luke's launcher task.

gradle/testing/alternative-jdk-support.gradle

@@ -85,5 +85,6 @@ if (jvmGradle != jvmCurrent) {
 }
 
 // Set up root project's properties.
+rootProject.ext.runtimeJavaExecutable = jvmCurrent.javaExecutable
 rootProject.ext.runtimeJavaHome = jvmCurrent.javaHome
 rootProject.ext.runtimeJavaVersion = jvmDetector.getMetadata(jvmCurrent.javaHome).languageVersion

lucene/luke/build.gradle

@@ -133,13 +133,8 @@ task run() {
 
   doFirst {
     logger.lifecycle("Launching Luke ${project.version} right now...")
-    def javaExecutable = {
-      def registry = project.extensions.getByType(JavaInstallationRegistry)
-      def currentJvm = registry.installationForCurrentVirtualMachine.get()
-      currentJvm.getJavaExecutable().asFile
-    }()
     ant.exec(
-        executable: javaExecutable,
+        executable: rootProject.ext.runtimeJavaExecutable,
         spawn: true,
         vmlauncher: true
     ) {