Merge bitcoin/bitcoin#28322: ci: Use concurrency for pull requests only

e7d67ef ci: Use concurrency for pull requests only (Hennadii Stepanov)

Pull request description:

  This PR is an amendment for bitcoin/bitcoin#28282.

  It avoids skipping builds when some pushes were done consequentially:

  ![image](https://github.com/bitcoin/bitcoin/assets/32963518/977e9ead-1856-4020-82eb-d16dbead5753)

  From GitHub Actions [docs](https://docs.github.com/en/actions/using-jobs/using-concurrency):

  > When a concurrent ... workflow is queued, if another ... workflow using the same concurrency group in the repository is in progress, the queued ... workflow will be pending. **Any previously pending ... workflow in the concurrency group will be canceled.**

  No behavior change for pull requests:

  ![image](https://github.com/bitcoin/bitcoin/assets/32963518/4865ae04-fc42-4028-b91e-500c0b36bce6)

ACKs for top commit:
  MarcoFalke:
    review only ACK e7d67ef
  dergoegge:
    lgtm ACK e7d67ef

Tree-SHA512: 360be9dbb46354d988935643e8793ea630c3416609c45aab4c39075a00a427487446a34a4fb93b490ece43cabe43640fcc6fb2ac97760e2c6ee54b95241da826

.github/workflows/ci.yml

@@ -14,8 +14,8 @@ on:
       - '**'
 
 concurrency:
-  group: ${{ github.ref }}
-  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+  group: ${{ github.event_name != 'pull_request' && github.run_id || github.ref }}
+  cancel-in-progress: true
 
 env:
   DANGER_RUN_CI_ON_HOST: 1