Skip benchmarking CI on forks (#688)

Co-Authored-By: Mosè Giordano <765740+giordano@users.noreply.github.com>

Author: christiangnrd

.github/workflows/benchmark_pr.yml

@@ -1,7 +1,7 @@
 name: Benchmark a pull request
 
 on:
-  pull_request:
+  pull_request_target:
 
 permissions:
   pull-requests: write