Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Fix truncating and batch backends integration.

Truncating backend was not starting batch thread that is responsible for reading events from the channel.

Fixes https://github.com/kubernetes/kubernetes/pull/65819

```release-note
None
```