Fix native initialization for ESTestCase (elastic#107203)

This tweaks the idea specific setup for multi java version projects to only ignore those in idea
when importing and syncing the project so we keep those sourcesets not imported to idea by default but
picked up when triggering (gradle) test execution (where idea.active = true)

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/MrjarPlugin.java

@@ -62,13 +62,13 @@ public class MrjarPlugin implements Plugin<Project> {
     public void apply(Project project) {
         project.getPluginManager().apply(ElasticsearchJavaBasePlugin.class);
         var javaExtension = project.getExtensions().getByType(JavaPluginExtension.class);
-        var isIdea = System.getProperty("idea.active", "false").equals("true");
+        var isIdeaSync = System.getProperty("idea.sync.active", "false").equals("true");
         var ideaSourceSetsEnabled = project.hasProperty(MRJAR_IDEA_ENABLED) && project.property(MRJAR_IDEA_ENABLED).equals("true");
 
         // Ignore version-specific source sets if we are importing into IntelliJ and have not explicitly enabled this.
         // Avoids an IntelliJ bug:
         // https://youtrack.jetbrains.com/issue/IDEA-285640/Compiler-Options-Settings-language-level-is-set-incorrectly-with-JDK-19ea
-        if (isIdea == false || ideaSourceSetsEnabled) {
+        if (isIdeaSync == false || ideaSourceSetsEnabled) {
             List<Integer> mainVersions = findSourceVersions(project);
             List<String> mainSourceSets = new ArrayList<>();
             mainSourceSets.add(SourceSet.MAIN_SOURCE_SET_NAME);