Incorrect arguments passed for running bench fix #1164

.github/workflows/ci-nix.yaml

@@ -143,7 +143,7 @@ jobs:
             options: 'datasets datasets/3-nodes.json datasets/1-node.json --output-directory $(pwd)/../benchmarks --timeout 1000s'
           - package: plutus-merkle-tree
             bench: on-chain-cost
-            options: '--output-directory $(pwd)/../benchmarks'
+            options: '$(pwd)/../benchmarks'
     steps:
     - name: 📥 Checkout repository
       uses: actions/checkout@v4