workflows: upload nixos test output

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>

.gitea/workflows/nix.yml

@@ -23,4 +23,13 @@ jobs:
           enable_kvm: true
 
       - name: Run tests
-        run: nix --print-build-logs --experimental-features 'nix-command flakes' flake check --all-systems
+        run: |
+          nix --print-build-logs --experimental-features 'nix-command flakes' flake check --all-systems
+          nix build --out-link "result" --print-out-paths --print-build-logs .#checks.x86_64-linux.nixos-tests
+
+      - name: Upload test output
+        uses: actions/upload-artifact@v3
+        with:
+          name: "result"
+          path: result/*
+          retention-days: 1