bench: cancel current job on new commits

Author: franckgaga

.github/workflows/benchmark.yml

@@ -2,6 +2,11 @@ name: Benchmark
 on:
   pull_request_target:
     branches: [ main ]
+concurrency:
+  # Skip intermediate builds: always.
+  # Cancel intermediate builds: only if it is a pull request build.
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: ${{ startsWith(github.ref, 'refs/pull/') }}
 permissions:
   pull-requests: write    # needed to post comments
 jobs: