fix(ci): add pull-requests write permission for benchmark alerts

The benchmark-action needs pull-requests:write to comment on PRs
when performance regressions are detected.

Author: tobyhede

.github/workflows/benchmark.yml

@@ -16,6 +16,8 @@ permissions:
   deployments: write
   # contents permission to update benchmark contents in gh-pages branch
   contents: write
+  # pull-requests permission to comment on PRs with benchmark alerts
+  pull-requests: write
 
 jobs:
   benchmark: