fix cache key

Author: MarshalX

.github/workflows/benchmark.yml

@@ -48,7 +48,7 @@ jobs:
         uses: actions/cache@v4
         with:
           path: ./benchmark-data
-          key: benchmark-${{ runner.os }}-${{ github.ref }}
+          key: benchmark-${{ runner.os }}-${{ github.base_ref || github.ref }}
 
       - name: Benchmark results
         uses: benchmark-action/github-action-benchmark@v1