Attestation commit code review feedback from #8794

[alexr00]

#8794

[Copilot]

Pull request overview

This PR refines how the PR timeline “New commits since your last review” marker is inserted, avoiding misleading markers when the only diverging commit predates the user’s latest review (e.g., an attestation commit), and aligns tests/documentation and a small caching initialization with that behavior.

Changes:

• Skip inserting the NewCommitsSinceReview marker when there are no commits after the user’s most recent review.
• Update the related unit test to assert that no marker is inserted in the pre-review-only diverging commit case.
• Improve attestation commit signing detection by treating commit.gpgsign as a Git boolean (truthy values), and remove an unnecessary empty-array initialization for cached PR timeline events.

Show a summary per file

File	Description
src/github/utils.ts	Changes marker insertion logic to return early (no marker) when no post-review commits are present.
src/test/github/utils.test.ts	Updates expectations to ensure no marker is inserted when the only diverging commit is pre-review.
src/issues/userCompletionProvider.ts	Removes redundant initialization of cachedPrTimelineEvents to [], leaving it undefined until populated.
src/github/attestationCommit.ts	Treats commit.gpgsign as a truthy Git boolean and updates inline documentation accordingly.

Copilot's findings

• Files reviewed: 4/4 changed files
• Comments generated: 0