Clarify the existing pending job is canceled (#34657)

Co-authored-by: Alex Nguyen <[email protected]>

data/reusables/actions/actions-group-concurrency.md

@@ -1,4 +1,4 @@
-When a concurrent job or workflow is queued, if another job or workflow using the same concurrency group in the repository is in progress, the queued job or workflow will be `pending`. Any pending job or workflow in the concurrency group will be canceled.  This means that there can be at most one running and one pending job in a concurrency group at any time.
+This means that there can be at most one running and one pending job in a concurrency group at any time. When a concurrent job or workflow is queued, if another job or workflow using the same concurrency group in the repository is in progress, the queued job or workflow will be `pending`. Any existing `pending` job or workflow in the same concurrency group, if it exists, will be canceled and the new queued job or workflow will take its place.
 
 To also cancel any currently running job or workflow in the same concurrency group, specify `cancel-in-progress: true`.  To conditionally cancel currently running jobs or workflows in the same concurrency group, you can specify `cancel-in-progress` as an expression with any of the allowed expression contexts.