update test workflow

.forgejo/workflows/test.yaml

@@ -2,17 +2,13 @@ on: [push, pull_request]
 name: Test
 jobs:
   test:
-    runs-on: node20
+    runs-on: nixos
     env:
       ZIG_LOCAL_CACHE_DIR: /zig/local-cache
       ZIG_GLOBAL_CACHE_DIR: /zig/global-cache
     steps:
       - name: Checkout
         uses: actions/checkout@v4.1.7
-      - name: Setup Nix
-        uses: https://github.com/cachix/install-nix-action@v27
-        with:
-          nix_path: nixpkgs=channel:nixos-unstable
       - name: Test
         run: nix develop .#default -c zig build test