Merge bitcoin/bitcoin#28282: ci: Ensure that only a single workflow processes github.ref at a time

0080b5650e ci: Ensure that only a single workflow processes `github.ref` at a time (Hennadii Stepanov)

Pull request description:

  This PR ensures that only a single workflow processes any push or pull request at a time.

  A new push will be queued (including the master branch).

  For a new pull request update, the previous in-progress one will be cancelled.

  Address https://github.com/bitcoin/bitcoin/pull/28187#discussion_r1295144563.

ACKs for top commit:
  dergoegge:
    utACK 0080b5650e

Tree-SHA512: d03f1678c93c817c1c3be5e75171bfe85d494f99a9aab7113c9438e0c820e950edd5c10199cccd54868e6dc50217bb3aa5601b23bc88ad4927c001031e917513

.github/workflows/ci.yml

@@ -13,6 +13,10 @@ on:
     tags-ignore:
       - '**'
 
+concurrency:
+  group: ${{ github.ref }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
 env:
   DANGER_RUN_CI_ON_HOST: 1
   TEST_RUNNER_TIMEOUT_FACTOR: 40