Backport of #26610 to release/v7.6

Triggered by @daxian-dbw on behalf of @daxian-dbw

Original CL Label: CL-BuildPackaging

/cc @PowerShell/powershell-maintainers

Impact

REQUIRED: Choose either Tooling Impact or Customer Impact (or both). At least one checkbox must be selected.

Tooling Impact

• Required tooling change
• Optional tooling change (include reasoning)

Customer Impact

• Customer reported
• Found internally

Tooling improvement for changelog generation. The Get-ChangeLog function now correctly handles backport PRs by extracting the real author from the PR body, ensuring proper attribution in changelogs.

Regression

REQUIRED: Check exactly one box.

• Yes
• No

This is not a regression.

Testing

The fix has been tested in the original PR. The changes can be verified by running Get-ChangeLog on a release branch that contains backport PRs and confirming that the changelog correctly attributes the commits to the original authors rather than the backport PR creators.

Risk

REQUIRED: Check exactly one box.

• High
• Medium
• Low

The changes only affect the changelog generation script used during the release process. It improves attribution accuracy for backport PRs by detecting them and extracting the real author from the PR body. This is tooling-only code that does not affect the product itself.