Skip benchmark PR comment for fork PRs

Fork PRs have read-only GITHUB_TOKEN and can't post comments.
Skip the find/create comment steps when PR is from a fork.
Benchmark comparison still runs and prints to console.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: mrecachinas

.github/workflows/benchmark.yml

@@ -285,6 +285,7 @@ jobs:
 
       - name: Find existing comment
         uses: peter-evans/find-comment@v3
+        if: github.event.pull_request.head.repo.full_name == github.repository
         id: find-comment
         with:
           issue-number: ${{ github.event.pull_request.number }}
@@ -293,6 +294,7 @@ jobs:
 
       - name: Create or update comment
         uses: peter-evans/create-or-update-comment@v4
+        if: github.event.pull_request.head.repo.full_name == github.repository
         with:
           comment-id: ${{ steps.find-comment.outputs.comment-id }}
           issue-number: ${{ github.event.pull_request.number }}