Update ci.yaml

add backend ci

.github/workflows/ci.yaml

@@ -49,3 +49,10 @@ jobs:
           cargo install --force duckscript_cli
           cargo make flowy_dev
           cargo make -p development-linux-x86 appflowy-linux-dev
+  build-backend:
+    runs-on: macOS-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Run backend tests
+        run: cd backend && cargo test