override: preserve status base SHA when overriding jobs

[SaaiAravindhRaja]

What type of PR is this?

/kind bug

What this PR does / why we need it:

When /override handles a failed presubmit status that already carries a BaseSHA: marker, it now reuses that original base SHA for both the replacement status description and the synthetic successful ProwJob.

This avoids replacing the job's original base SHA with the base branch SHA at command time, which can differ if the base branch moved after the job ran.

Which issue(s) this PR fixes:

Part of #789

Special notes for your reviewer:

This keeps the existing synthetic ProwJob behavior intact and only changes the base SHA source used when creating the override result.

Does this PR introduce a user-facing change?

NONE

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[kubernetes-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: SaaiAravindhRaja
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[kubernetes-prow]

Hi @SaaiAravindhRaja. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[ylink-lfs]

/ok-to-test

[SaaiAravindhRaja]

hi! is there anything i can improve on?

[Prucek]

I am not sure about this; isn't this solving the same issue: #778 ?