Add danger workflow

.github/workflows/danger.yml

@@ -0,0 +1,20 @@
+name: Danger CI
+
+on: [pull_request]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    name: Danger
+    steps:
+      - uses: actions/checkout@v3
+      - run: |
+          npm install --save-dev @babel/plugin-transform-flow-strip-types
+      - name: Danger
+        uses: danger/danger-js@11.2.0
+        with:
+          args: "--dangerfile ./tools/danger/dangerfile.js"
+        env:
+          DANGER_GITHUB_API_TOKEN: ${{ secrets.DANGER_GITHUB_API_TOKEN }}
+          # Fallback for forks
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}