ci: avoid duplicate benchmark workflows

Author: ajay-mk

.github/workflows/benchmark_compare.yml

@@ -10,6 +10,10 @@ on:
         required: true
         type: number
 
+concurrency:
+  group: benchmark-${{ github.event.issue.number || github.event.inputs.pr_number }}
+  cancel-in-progress: true
+
 jobs:
   benchmark:
     if: >