SpringBoot Event handling in JobExecutionExitCodeGenerator is not thread-safe

The listener could be invoked concurrently by multiple thread, we should make them threadsafe.

SimpleApplicationEventMulticaster doc:

By default, all listeners are invoked in the calling thread.

Comment From: dugenkui03

@wilkinsona Thanks for your review. Code in HibernateJpaAutoConfigurationTests have been reverted , please help review again.

Comment From: wilkinsona

Thanks very much, @dugenkui03. I separated out into a separate issue (#30844) the changes to ClassPathFileSystemWatcherTests as, unlike the problem with JobExecutionExitCodeGenereator, the problem with the tests won't affect users.