add a simple github action workflow to build test the documentation

Signed-off-by: Matthieu Gallien <[email protected]>

.github/workflows/documentation.yml

@@ -0,0 +1,22 @@
+name: Generate Documentation
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+jobs:
+  build:
+    name: Generate Documentation
+    runs-on: ubuntu-latest
+    container: ghcr.io/nextcloud/continuous-integration-client-qt6-doc:client-doc-6.8.0-1
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 1
+      - name: Generate documentation
+        run: |
+          cd doc
+          make html > build.log 2>&1
+          if grep WARNING build.log; then
+              exit 1
+          else
+              exit 0
+          fi