[log4j] CL leak in `ThrowableProxy` (#3282)

[Volkan Yazıcı]

Alan, do you have time to investigate #3282
<https://github.com/apache/logging-log4j2/issues/3282>, please? 😇

I see that your Slack guest account has been deactivated, I guess due to
expiration. 🤦 I will try to reactivate it.