chore: cancel running CI jobs if a new commit is pushed

We could apply something like this to cancel long running jobs like miri tests if we push multiple commits in succession: https://www.meziantou.net/how-to-cancel-github-workflows-when-pushing-new-commits-on-a-branch.htm ```yml concurrency: # github.workflow: name of the workflow # github.event.pull_request.number || github.ref: pull request number or branch name if not a pull request group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }} # Cancel in-progress runs when a new workflow with the same group name is triggered cancel-in-progress: true ```