Merge #1410: ci: Use concurrency for pull requests only

ee1be62 ci: Use concurrency for pull requests only (Hennadii Stepanov)

Pull request description:

  This PR is an amendment for #1403.

  It avoids skipping builds when some pushes were done consequentially.

  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.

  Same as bitcoin/bitcoin#28322.

ACKs for top commit:
  real-or-random:
    ACK ee1be62

Tree-SHA512: ce26378c3224a7647eb3b351d19e9308650ad49b933a68d37a0eca8516767a63f55580a33b02864caa539392c9aab0b4b54ecbace85bea6082bf533539a37c9c

.github/workflows/ci.yml

@@ -8,8 +8,8 @@ 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:
   ### compiler options