refactor: remove code smell java:S5786 (#2159)

https://sonarcloud.io/organizations/iluwatar/rules?open=java%3AS5786&rule_key=java%3AS5786

producer-consumer/src/test/java/com/iluwatar/producer/consumer/ConsumerTest.java

@@ -36,7 +36,7 @@ import org.junit.jupiter.api.Test;
  *
  * @author Jeroen Meulemeester
  */
-public class ConsumerTest {
+class ConsumerTest {
 
   private static final int ITEM_COUNT = 5;
 

producer-consumer/src/test/java/com/iluwatar/producer/consumer/ProducerTest.java

@@ -38,7 +38,7 @@ import org.junit.jupiter.api.Test;
  *
  * @author Jeroen Meulemeester
  */
-public class ProducerTest {
+class ProducerTest {
 
   @Test
   void testProduce() {