ci: move nix build to dedicated job

.github/workflows/test.yml

@@ -42,6 +42,29 @@ jobs:
       - name: Test Build
         run: nix develop -c zig build -Dstatic=true -Dapp-runtime=glfw -Dtarget=${{ matrix.target }}
 
+  build-nix:
+    strategy:
+      matrix:
+        os: [ubuntu-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      # Install Nix and use that to run our tests so our environment matches exactly.
+      - uses: cachix/install-nix-action@v24
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+
+      # Use cache to minimize build times.
+      - name: Setup Nix cache
+        uses: DeterminateSystems/magic-nix-cache-action@main
+        with:
+          diagnostic-endpoint: "" # disable telemetry
+
+      - name: Test NixOS package build
+        run: nix build .#ghostty
+
   build-macos:
     runs-on: ghcr.io/cirruslabs/macos-ventura-xcode:latest
     needs: test
@@ -73,6 +96,7 @@ jobs:
       # Nix breaks xcodebuild so this has to be run outside.
       - name: Build Ghostty.app
         run: cd macos && xcodebuild
+
   build-windows:
     runs-on: windows-2019
     # this will not stop other jobs from running
@@ -156,9 +180,6 @@ jobs:
       - name: Test Dynamic Build
         run: nix develop -c zig build -Dstatic=false
 
-      - name: Test NixOS package build
-        run: nix build .#ghostty
-
   prettier:
     runs-on: ubuntu-latest
     steps: