test: update benchmark pull request configuration

Author: brianheineman

.github/workflows/pr-benchmarks.yml

@@ -35,11 +35,13 @@ jobs:
         run: |
           cargo bench --bench archive --features blocking -- --output-format criterion | \
             bencher run \
+              --branch $GITHUB_HEAD_REF \
               --ci-number "${{ github.event.number }}" \
               --github-actions "${{ secrets.GITHUB_TOKEN }}" \
               --err
           cargo bench --bench embedded --features blocking -- --output-format criterion | \
             bencher run \
+              --branch $GITHUB_HEAD_REF \
               --ci-number "${{ github.event.number }}" \
               --github-actions "${{ secrets.GITHUB_TOKEN }}" \
               --err