ci(precheck): speed up precheck tests

.github/workflows/test-precheck.yaml

@@ -14,10 +14,10 @@ jobs:
 
     steps:
       - name: Check out code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Set up Python
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v4
         with:
           python-version: '3.11'
           cache: 'pip'
@@ -34,7 +34,17 @@ jobs:
           pdk_root: ${{ env.PDK_ROOT }}
 
       - name: Install nix
-        uses: cachix/install-nix-action@v20
+        uses: cachix/install-nix-action@v23
+
+      - name: Cache Nix packages
+        uses: rikhuijzer/[email protected]
+        with:
+          key: nix-${{ hashFiles('precheck/default.nix') }}
+          nix_file: 'precheck/default.nix'
+
+      - name: Build Nix packages
+        working-directory: precheck
+        run: nix-build
 
       - name: Run tests
         working-directory: precheck

precheck/default.nix

@@ -1,8 +1,4 @@
-{ pkgs ? import
-    (builtins.fetchGit {
-      url = "https://github.com/NixOS/nixpkgs.git";
-      rev = "f2bd8adf7b78d7616b52d0ef08865c7c2fcf189d";
-    })
+{ pkgs ? import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/f2bd8adf7b78d7616b52d0ef08865c7c2fcf189d.tar.gz")
     { }
 , magic ? import ./nix/magic.nix { inherit pkgs; }
 ,