Support getPermissions() call on Gradle 8.6-milestone-1

The `getPermissions` method is now part of the private
`ParentDirectoryStub` class so we now need to call
`setAccessible(true)`.

Fixes gh-38718

Author: philwebb

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/tasks/bundling/BootZipCopyAction.java

@@ -22,6 +22,7 @@
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.io.OutputStreamWriter;
+import java.lang.reflect.Method;
 import java.time.OffsetDateTime;
 import java.time.ZoneOffset;
 import java.util.Collection;
@@ -462,7 +463,9 @@ private int getFileMode(FileCopyDetails details) {
 		private int getPermissions(FileCopyDetails details) {
 			if (GradleVersion.current().compareTo(GradleVersion.version("8.3")) >= 0) {
 				try {
-					Object permissions = details.getClass().getMethod("getPermissions").invoke(details);
+					Method getPermissionsMethod = details.getClass().getMethod("getPermissions");
+					getPermissionsMethod.setAccessible(true);
+					Object permissions = getPermissionsMethod.invoke(details);
 					return (int) permissions.getClass().getMethod("toUnixNumeric").invoke(permissions);
 				}
 				catch (Exception ex) {