fix: resolve SonarCloud issue in dirty flag / App.java #2865 (#3236)

dirty-flag/src/main/java/com/iluwatar/dirtyflag/App.java

@@ -57,6 +57,7 @@ public class App {
   /** Program execution point. */
   public void run() {
     final var executorService = Executors.newSingleThreadScheduledExecutor();
+    try {
       executorService.scheduleAtFixedRate(
           new Runnable() {
             final World world = new World();
@@ -70,7 +71,16 @@ public class App {
           },
           0,
           15,
-        TimeUnit.SECONDS); // Run at every 15 seconds.
+          TimeUnit.SECONDS);
+
+      // Keep running for 45 seconds before shutdown (for demo purpose)
+      TimeUnit.SECONDS.sleep(45);
+    } catch (InterruptedException e) {
+      Thread.currentThread().interrupt();
+      LOGGER.error("Thread was interrupted", e);
+    } finally {
+      executorService.shutdown();
+    }
   }
 
   /**