Fix mistakenly inverted conditional (#90532)

A build is considered included in a composite if it has a parent. So
this should check of the parent is NOT null.

build-tools/src/main/java/org/elasticsearch/gradle/util/GradleUtils.java

@@ -228,6 +228,6 @@ public abstract class GradleUtils {
      * @return true if the project is an included build
      */
     public static boolean isIncludedBuild(Project project) {
-        return project.getGradle().getParent() == null;
+        return project.getGradle().getParent() != null;
     }
 }