cancel the previous CI/CD unfinished tests if a pull request updated

[wyli]

every commit to an existing pull request will create a new set of ci/cd jobs. but normally we just wanted to test the branch's latest version. Any unfinished previous testing jobs could be cancelled immediately when a pull request updated. This will release self-hosted machine resources and improve the overall dev efficiency

perhaps could use this https://github.com/styfle/cancel-workflow-action

mainly for the per PR self-hosted job: https://github.com/Project-MONAI/MONAI/blob/master/.github/workflows/pythonapp.yml#L154

[rijobro]

definitely a great thing to sort out!

[wyli]

#1502 doesn't work from a forked repo, I'm reopening this ticket