Brief summary of the bug. What is it ? Where is it ?

When issues occur during backup creation, such as Optimize trying to trigger a backup with the same ID already being in progress, the exceptions thrown in our async listener methods can trigger the following issue: https://github.com/elastic/elasticsearch/issues/45115

This should also be backported to 39.

Steps to reproduce:

Exceptions occur during backup creation.

Actual result:

https://github.com/elastic/elasticsearch/issues/45115

Expected result:

Errors should be logged, but exceptions should not be rethrown in async methods.

Testing Notes:
This is not testable because it is hard to reproduce.