SpringBoot Relax ConfigFileApplicationListener.onApplicationEvent() to log a warning rather than throw an exception

Spring Cloud is deprecating its usage of ConfigFileApplicationListener, but it still needs to work.

/cc @philwebb

Comment From: spencergibb

Related #22601

Comment From: spencergibb

Since the usage wasn't via spring.factories, a subclass that overrides the onApplicationEvent() to not throw an exception works.