some snippets for github actions

gh-actions-configuring.yml

# Cancel workflow if new workflow in same group is in progress.
# https://docs.github.com/en/enterprise-cloud@latest/actions/using-jobs/using-concurrency
name: Build
concurrency:
  group: build-${{ github.ref }}
  cancel-in-progress: true 

# allow only certain types of pull_request.
pull_request:
    types: [ opened, reopened, synchronize ]