cancel unfinished CI run to save CI time (#5006)

This cancels the ci for previous commits on the same branch and previous commits in a PR, which should save CI time since the CI builds do no longer stack up when pushing multiple times while the CI is still running.

.github/workflows/ci.yml

@@ -2,6 +2,10 @@ name: CI
 
 on: [push, pull_request]
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 jobs:
   ci:
     strategy: