Add more unit test for BootstrapArguments

[FlyingZC]

Hi community,

This issue is for https://github.com/apache/shardingsphere/issues/20305.

Aim

Add more unit tests for BootstrapArguments to test its public functions to improve unit test coverage.

Unit test coverage can be viewed at: https://app.codecov.io/gh/apache/shardingsphere

Basic Qualifications

Java Maven Junit