ci: lower Codspeed CUDA runner CPU count (vortex-data#8130)

## Summary
- keep CUDA Codspeed benchmarks on g5 runners
- request 8 CPU cores for the GPU runner

Signed-off-by: Alexander Droste <alexander.droste@protonmail.com>

Author: 0ax1

.github/workflows/codspeed.yml

@@ -76,7 +76,8 @@ jobs:
           - { shard: 3, name: "Standalone kernels", benches: "alp_cuda date_time_parts_cuda dict_cuda fsst_cuda runend_cuda" }
     name: "Benchmark with Codspeed (CUDA Shard #${{ matrix.shard }} - ${{ matrix.name }})"
     timeout-minutes: 30
-    runs-on: runs-on=${{ github.run_id }}/family=g5/image=ubuntu24-gpu-x64/tag=bench-codspeed-cuda-${{ matrix.shard }}
+    runs-on: >-
+      runs-on=${{ github.run_id }}/family=g5/cpu=8/image=ubuntu24-gpu-x64/tag=bench-codspeed-cuda-${{ matrix.shard }}
     steps:
       - uses: runs-on/action@v2
         with: