✨ Set up and enable Material for MkDocs Insiders for the docs (#2325)

* ⬆️ Upgrade Material for MkDocs

* ⬆️ Install Material for MkDocs Insiders on CI

* 🔧 Update MkDocs configs to use Material for MkDocs Insiders

* ✨ Use the lightbulb because it looks nice 💡

* 💚 Fix GitHub Action workflow syntax for building docs

* 🐛 Fix GitHub Actions workflow syntax, strike one ⚾

.github/workflows/build-docs.yml

@@ -20,6 +20,9 @@ jobs:
         run: python3.7 -m pip install flit
       - name: Install docs extras
         run: python3.7 -m flit install --extras doc
+      - name: Install Material for MkDocs Insiders
+        if: github.repository == 'tiangolo/fastapi'
+        run: pip install git+https://${{ secrets.ACTIONS_TOKEN }}@github.com/squidfunk/mkdocs-material-insiders.git
       - name: Build Docs
         run: python3.7 ./scripts/docs.py build-all
       - name: Zip docs