Fix actions/jekyll-build-pages

Attempt to fix https://github.com/FreshRSS/FreshRSS/issues/5721

.github/workflows/jekyll-gh-pages.yml

@@ -33,7 +33,7 @@ jobs:
       - name: Build with Jekyll
         uses: actions/jekyll-build-pages@v1
         with:
-          source: ./
+          source: ./docs/
           destination: ./_site
       - name: Upload artifact
         uses: actions/upload-pages-artifact@v2