Revise JdbcChatMemoryRepository tests

[quaff]

1. Fix failed JdbcChatMemoryRepositoryPostgresqlIT tests due to connection leakage:

org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection

	at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:84)
	at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:653)
	at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:723)
	at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:754)
	at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:767)
	at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:820)
	at org.springframework.jdbc.core.JdbcTemplate.queryForList(JdbcTemplate.java:954)
	at org.springframework.ai.chat.memory.repository.jdbc.AbstractJdbcChatMemoryRepositoryIT.saveMessagesMultipleMessages(AbstractJdbcChatMemoryRepositoryIT.java:103)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
Caused by: java.sql.SQLTransientConnectionException: HikariPool-1 - Connection is not available, request timed out after 30001ms (total=10, active=10, idle=0, waiting=0)
	at com.zaxxer.hikari.pool.HikariPool.createTimeoutException(HikariPool.java:686)
	at com.zaxxer.hikari.pool.HikariPool.getConnection(HikariPool.java:179)
	at com.zaxxer.hikari.pool.HikariPool.getConnection(HikariPool.java:144)
	at com.zaxxer.hikari.HikariDataSource.getConnection(HikariDataSource.java:127)
	at org.springframework.jdbc.datasource.DataSourceUtils.fetchConnection(DataSourceUtils.java:160)
	at org.springframework.jdbc.datasource.DataSourceUtils.doGetConnection(DataSourceUtils.java:118)
	at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:81)
	... 10 more

2. Remove unnecessary tests, correctChatMemoryRepositoryInstance() do nothing, repositoryWithExplicitTransactionManager() actually doesn't test explicit transaction manager

[quaff]

@sunyuhan1998 I notice some test code committed by you, could you take a look?

[markpollack]

Hi. I did not have failures in JdbcChatMemoryRepositoryPostgresqlITcan you explain more what you observed.

[markpollack]

Thanks so much. 🍺

merged in b83a162