[3.5] fix(defrag): handle errors during defrag

[ghouscht]

Backport of https://github.com/etcd-io/etcd/pull/18822 to 3.5.

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

[k8s-ci-robot]

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[ghouscht]

@ahrtr PR for the 3.5 backport. Should I squash the commits into one?

[ahrtr]

/ok-to-test

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ahrtr, ghouscht, serathius

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/etcd-io/etcd/blob/release-3.5/OWNERS)~~ [ahrtr,serathius] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[ivanvc]

Link to #18810