fix(bench): use bench scripts from main, not PR branch

The workflow checks out the PR head ref for building, but this means
bench scripts come from the PR branch which may not have the latest
infrastructure changes (e.g. baseline-args/feature-args support).

Overlay bench scripts from origin/main after checkout so the benchmark
infrastructure is always up to date regardless of the PR being tested.

Co-Authored-By: Alexey Shekhirin <5773434+shekhirin@users.noreply.github.com>

.github/workflows/bench.yml

@@ -498,6 +498,12 @@ jobs:
           fetch-depth: 0
           ref: ${{ steps.checkout-ref.outputs.ref }}
 
+      # The checkout above uses the PR head ref, so .github/scripts/
+      # may be outdated. Overlay the bench scripts from main so the
+      # benchmark infrastructure always uses the latest version.
+      - name: Update bench scripts from main
+        run: git checkout origin/main -- .github/scripts/bench-*
+
       - name: Resolve job URL and update status
         if: env.BENCH_COMMENT_ID
         uses: actions/github-script@v8