pac concurrency scheduler don't clear up existing Pending PipelineRuns

[chmouel]

• create a repo with a concurrency_limit of 1 (or other number)
• start pipelines-as-code and take down the watcher (by scaling it down)
• create a PR with a few PipelineRun in there.
• observe that the PRs get queued as Pending by the controller.
• start the watcher.

The watcher get stuck and don't clear up the Q of the Pending PipelineRuns