🔧 Split MkDocs insiders build in CI to support building from PRs (#186)

.github/workflows/build-docs.yml

@@ -56,7 +56,11 @@ jobs:
           key: mkdocs-cards-${{ github.ref }}
           path: .cache
       - name: Build Docs
+        if: github.event.pull_request.head.repo.fork == true
         run: python -m poetry run mkdocs build
+      - name: Build Docs with Insiders
+        if: github.event.pull_request.head.repo.fork == false
+        run: python -m poetry run mkdocs build --config-file mkdocs.insiders.yml
       - name: Zip docs
         run: python -m poetry run bash ./scripts/zip-docs.sh
       - uses: actions/upload-artifact@v2