ci: exempt master branch workflows from getting cancelled (#6486)

* ci: exempt master branch workflows from getting cancelled

* apply to bench.yml

.github/workflows/zig-build.yml

@@ -7,7 +7,7 @@ on:
       - master
 
 concurrency:
-  group: ${{ github.workflow }}-${{ github.ref }}
+  group: ${{ github.workflow }}-${{ github.head_ref && github.ref || github.run_id }}
   cancel-in-progress: true
 
 jobs: