Fix status check deduplication dropping checks from different workflow events

[Copilot]

When the same workflow triggers on both push and pull_request, the resulting check runs share the same name but are distinct checks. deduplicateStatusChecks keyed only on context (the check run name), collapsing e.g. 4 checks into 2.

Changes

• src/github/githubRepository.ts: Include event and workflowName in the deduplication key so checks from different trigger events or different workflows are preserved:

  const key = `${status.context}\0${status.event ?? ''}\0${status.workflowName ?? ''}`;

  Re-runs of the same check (same name + event + workflow) are still correctly deduplicated.

• src/test/github/githubRepository.test.ts: Added tests covering different events kept separate, same-event deduplication, different workflows kept separate, and pending-over-completed preference.