Minimize comment noise in maintainer-approval workflow

[simonfaltum]

Why

The maintainer-approval GitHub Action deletes and recreates its PR comment on every push, review change, and reopen event. Each delete+create cycle sends notifications to all participants, creating unnecessary noise. Approval state comments ("Approved by @user") are also redundant since the commit status already conveys that information.

Changes

Before: every workflow run deletes the old comment and posts a new one, even if nothing changed. Approval events post dedicated "Approved by" comments.

Now: the workflow edits the existing comment in place (no notification), skips the edit entirely when the body hasn't changed, and stops posting approval comments. On approval, any stale pending comment is cleaned up so the PR doesn't show a misleading "Waiting for approval" alongside a green status.

Specifically:

• Replaced postComment (delete+create) with upsertComment (find, compare, edit-in-place)
• Removed buildApprovedComment and buildAllGroupsApprovedComment (commit status is sufficient)
• All three success paths (maintainer approval, maintainer-authored, all groups approved) now only set commit status and clean up stale marker comments
• Added deleteMarkerComments helper for success-path cleanup

Test plan

• All 20 unit tests pass (node --test .github/workflows/maintainer-approval.test.js)
• Tests cover: create when none exists, edit in place, skip when unchanged, duplicate cleanup, stale comment cleanup on approval, no-comment on all success paths

This pull request was AI-assisted by Isaac.

[github-actions]

Approved (maintainer-authored PR)

_{See OWNERS for ownership rules.}