fix: resolve maven build failure

Author: anshullakra007

src/main/java/com/thealgorithms/sorts/ConcurrentMergeSort.java

@@ -22,7 +22,7 @@
  *   <li>Space Complexity: $O(N)$</li>
  * </ul>
  */
-public class ConcurrentMergeSort {
+public final class ConcurrentMergeSort {
 
     private ConcurrentMergeSort() {
     }