Prior to this commit, `ResourceUrlProvider` would listen and consider
all `ContextRefreshedEvent` and use the given context to detect
`SimpleUrlHandlerMapping`.
This could lead to situations where a `ResourceUrlProvider` uses another
application context than its own (in a parent/child context setup) and
detect the wrong set of handlers.
Because `ResourceUrlProvider` locks itself once the auto-detection is
done, we need to ensure that it considers only events sent by its
application context.
Fixes gh-26561
947387b4cd