build-in-devcontainer: not cancellable in the GitHub UI?

Description

Today, I observed something like this on a cudf PR:

1. apply a suggestion from the GitHub UI (that creates a new commit)
2. immediately after, click "update branch" in the GitHub UI (created a new merge commit pulling in latest main)
3. observe all jobs on the CI run from the first commit auto-cancelled except devcontainer jobs
4. try to manually cancel the old workflow run by clicking "Cancel Workflow"
5. GitHub UI says "You have successfully requested the workflow to be cancelled"
6. devcontainer jobs not cancelled (even after 10 minutes), next CI run stuck in Pending until they finished

I don't know if this was GitHub issue (temporary or permanent), specific to the build-in-devcontainer workflow (maybe it doesn't respect OS signals?) or something else... just opening to track.

Notes

Details:

• original observation: https://github.com/rapidsai/cudf/pull/21464#issuecomment-3928482517
• runs: https://github.com/rapidsai/cudf/actions/workflows/pr.yaml?query=branch%3Apull-request%2F21464

Start with the build-in-devcontainer jobs in the shared workflow and compare their cancellation behavior with the other jobs in pr.yaml. Reproduce or inspect the runs linked from cudf PR #21464, then determine whether cancelling the old workflow stops those jobs and prevents the next run from remaining Pending.