[ci] Set CodSpeedHQ/action's mode to simulation

v4 requires the mode to me explicitly set.

Author: gruenich

.github/workflows/codspeed-bench.yml

@@ -149,6 +149,7 @@ jobs:
       - name: Run benchmarks
         uses: CodSpeedHQ/action@v4
         with:
+          mode: simulation
           token: ${{ secrets.CODSPEED_TOKEN }}
           run: |
             cd benchmark/pybench