Adjust MyBatisSystemException to Spring 6

[harawata]

Since Spring 6, org.springframework.core.NestedRuntimeException no longer includes the message of the wrapped exception.
spring-projects/spring-framework#25162

Should fix gh-887

[coveralls]

coverage: 89.689% (+0.06%) from 89.633%
when pulling d349069 on harawata:gh/887
into bc7e285 on mybatis:master.

[kazuki43zoo]

@harawata Thanks!!
I added a few comment, please confirm when you have a time.

[harawata]

@kazuki43zoo ,

Thanks for the review!
I added a series of tests for MyBatisExceptionTranslator.

---

FYI, while writing the tests, I noticed that TransactionException is not a subclass of DataAccessException.

spring/src/main/java/org/mybatis/spring/MyBatisExceptionTranslator.java

Lines 94 to 96 in f53cfce

	} else if (e.getCause() instanceof TransactionException) {
	throw (TransactionException) e.getCause();
	}

Unfortunately, this part is not covered by tests, but it was added as a fix for #115 , it seems.
It might be worth looking into.

Sorry, TransactionException was thrown, not returned, so it should be fine.

[kazuki43zoo]

LGTM!