When a GitHub Actions workflow uses concurrency with cancel-in-progress,
cancelled runs were counted as failures in `gh pr status` and
`gh pr view`, even when a newer run for the same check name succeeded.
The GitHub web UI and `gh pr checks` both handle this correctly.
Three changes fix this:
1. Add a `cancelled` check status category. Cancelled runs are now
excluded from all summary counts (passing/failing/pending) and
subtracted from the total, matching the web UI behavior.
2. Move `eliminateDuplicates` from pkg/cmd/pr/checks to
`api.EliminateDuplicateChecks` (exported). The function operates
entirely on `api.CheckContext` and is now shared by both `pr checks`
and `ChecksStatus()` (used by `pr status` and `pr view`).
3. Apply deduplication in the `ChecksStatus()` slow path, keeping only
the most recent run per check name — consistent with `pr checks`.
Fixes#12895
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>