ci: attribute scheduled and flaky test failures to the originating commit

When a scheduled workflow or flaky test fails, there is no link between the failure and the commit that introduced it. QA collects and reports on these failures, but addressing them is not a visible development priority because the failure doesn't appear on the commit itself — it only appears on the scheduled run.

Proposal: use an alternate GitHub token to retroactively post a commit status or check run against the specific commit that first introduced the regression. This surfaces the failure where it landed rather than where the scheduled job happened to run, making it harder to defer.

This would replace the current model of collecting test failure reports, by assigning error states directly to the responsible commits on GitHub.