Only run benchmarks on merge to main

Author: si618

.github/workflows/workflow.yml

@@ -38,6 +38,7 @@ jobs:
 
   benchmark:
     needs: [ build ]
+    if: github.event_name == 'push' && github.ref == 'refs/heads/main'
     runs-on: ubuntu-latest
     steps:
       - name: Checkout