CI: Automatically cancel old workflow runs on PRs

[btashton]

We can be a little less wasteful of our limited runner resources by having old runs for PRs get automatically cancelled when new runs on the PR are triggered. This usually happens when someone creates a PR and then it runs and while it is running improvements are made to it. The new run then sits until the old run fails or completes which can take 1hr+ especially with the macOS runners.

This has been discussed a bit on the Apache builds mailing list and the Apache Airflow project which uses GitHub actions extensively used this action to automate this https://github.com/apache/airflow-cancel-workflow-runs

There is also a max concurrency across the whole Apache GitHub organization so heavy use of the runners can impact other projects as well.