ci(docs): only upload artifacts when html output exists

Author: woxxy

.github/workflows/docs.yml

@@ -46,15 +46,15 @@ jobs:
         run: sphinx-build --fail-on-warning --keep-going -b html docs docs/_build/html
 
       - name: Upload docs artifact (PR/debug)
-        if: always()
+        if: always() && hashFiles('docs/_build/html/**') != ''
         uses: actions/upload-artifact@v4
         with:
           name: docs-html
           path: docs/_build/html
-          if-no-files-found: error
+          if-no-files-found: warn
 
       - name: Upload Pages artifact
-        if: github.event_name == 'push' && github.ref == format('refs/heads/{0}', github.event.repository.default_branch)
+        if: github.event_name == 'push' && github.ref == format('refs/heads/{0}', github.event.repository.default_branch) && hashFiles('docs/_build/html/**') != ''
         uses: actions/upload-pages-artifact@v3
         with:
           path: docs/_build/html