ci: Update benchmark workflow to Zig 0.16.0

The benchmark was failing because it was still using Zig 0.15.1
but the codebase has been migrated to 0.16.

Refs #89

Author: justrach

.github/workflows/benchmark.yml

@@ -18,10 +18,10 @@ jobs:
       - name: Checkout merjs
         uses: actions/checkout@v4
 
-      - name: Setup Zig 0.15.1
+      - name: Setup Zig 0.16.0
         uses: mlugg/setup-zig@v2
         with:
-          version: 0.15.1
+          version: 0.16.0
 
       - name: Setup Node.js 20
         uses: actions/setup-node@v4