wait on demo build to succeed

.github/workflows/demo.yml

@@ -3,18 +3,31 @@ name: Demo
 on:
   workflow_dispatch:
   pull_request:
-    paths:
-      - '.github/workflows/demo.yml'
-      - 'demo/**'
   push:
     branches:
       - main
-    paths:
-      - '.github/workflows/demo.yml'
-      - 'demo/**'
 
 jobs:
+  path-filter:
+    runs-on: ubuntu-latest
+    outputs:
+      changed: ${{ steps.filter.outputs.changed }}
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - uses: dorny/paths-filter@v3
+        id: filter
+        with:
+          filters: |
+            changed:
+              - '.github/workflows/demo.yml'
+              - 'demo/**'
+
   build:
+    needs: [ "path-filter" ]
+    if: needs.path-filter.outputs.changed == 'true'
     strategy:
       matrix:
         demo:
@@ -53,4 +66,15 @@ jobs:
             --show-trace \
             build .#nixosConfigurations.${{ matrix.demo.flake }}.config.system.build.vm
 
-
+  result:
+    runs-on: ubuntu-latest
+    needs: [ "build" ]
+    if: '!cancelled()'
+    steps:
+      - run: |
+          result="${{ needs.tests.result }}"
+          if [[ $result == "success" || $result == "skipped" ]]; then
+            exit 0
+          else
+            exit 1
+          fi