Fix benchmark CI working directory

Author: SaridakisStamatisChristos

.github/workflows/ci.yml

@@ -35,6 +35,7 @@ jobs:
           python -m pip install --upgrade pip
           python -m pip install -e './kll_sketch[bench]'
       - name: Run smoke benchmark
+        working-directory: ${{ github.workspace }}
         run: |
           python benchmarks/bench_kll.py \
             --outdir bench_out \