style: add newline at end of files

Author: gowtham1412-p

src/main/java/com/thealgorithms/datastructures/stacks/StackUsingLinkedList.java

@@ -210,4 +210,4 @@ public static void main(String[] args) {
         System.out.println("Stack after clear: " + stack);
         System.out.println("Is empty? " + stack.isEmpty());
     }
-}
+}

src/test/java/com/thealgorithms/datastructures/stacks/StackUsingLinkedListTest.java

@@ -100,4 +100,4 @@ void testSingleElement() {
         assertEquals(42, stack.pop());
         assertTrue(stack.isEmpty());
     }
-}
+}