Backport of #26415 to release/v7.6

Triggered by @adityapatwardhan on behalf of @TravisEz13

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)

This change is required for proper handling of rebuild branches in the release pipeline. It prevents LTS packages from being incorrectly built and published from rebuild branches, and adds conditional MSIX signing for official builds only. Without this backport, rebuild branches for v7.6 would not have the proper safety checks in place.

Customer Impact

• Customer reported
• Found internally

Regression

REQUIRED: Check exactly one box.

• Yes
• No

This is not a regression.

Testing

The original PR was tested on master branch with rebuild branch scenarios. For backport verification: (1) Confirmed all modified templates compile without syntax errors, (2) Verified cherry-pick applied all intended changes correctly, (3) Conflict resolution preserved the enhanced logging functionality from the original PR. Full CI testing will validate the rebuild branch detection logic and conditional MSIX signing behavior.

Risk

REQUIRED: Check exactly one box.

• High
• Medium
• Low

This backport affects build and packaging pipelines across multiple platforms. While the changes are well-contained and add safety checks for rebuild branches, any modifications to CI/CD infrastructure carry inherent risk. The changes include conditional logic that could affect package generation, but the logic is defensive and designed to prevent incorrect package builds.

Merge Conflicts

Merge conflict in .pipelines/templates/package-create-msix.yml: Release branch had simplified variable setting, PR added verbose logging. Resolved by applying the enhanced version with verbose logging from the original PR.