Control concurrency and cancel in-progress runs when re-triggered.

.github/workflows/benchmark.yml

@@ -7,6 +7,10 @@ on:
     workflows: [Test]
     types: [completed]
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.workflow_run.head_branch }}
+  cancel-in-progress: true
+
 jobs:
   benchmark:
     runs-on: ubuntu-24.04