ci: use dart format

Author: jpnurmi

.github/workflows/analyze.yml

@@ -29,7 +29,7 @@ jobs:
       - name: Install dependencies
         run: flutter pub get
       - name: Format
-        run: flutter format --set-exit-if-changed .
+        run: dart format --set-exit-if-changed .
 
   publish:
     runs-on: ubuntu-latest