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

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

monitor/src/test/java/com/iluwatar/monitor/BankTest.java

@@ -30,7 +30,7 @@ import org.junit.jupiter.api.Test;
 import static org.junit.jupiter.api.Assertions.*;
 import static org.junit.jupiter.api.Assumptions.*;
 
-public class BankTest {
+class BankTest {
 
   private static final int ACCOUNT_NUM = 4;
   private static final int BASE_AMOUNT = 1000;