RFR: Fixed backing out a backport [v2]

[Iris Clark]

On Mon, 13 Oct 2025 22:56:55 GMT, Jesper Wilhelmsson <jwilhelm at openjdk.org> wrote:

>> Backing out a change was updated to not use sub-tasks, but the similar case of backing out a backport was missed.
>
> Jesper Wilhelmsson has updated the pull request incrementally with one additional commit since the last revision:
> 
>   O to I

Marked as reviewed by iris (Reviewer).

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PR Review: https://git.openjdk.org/guide/pull/160#pullrequestreview-3334001208