ci: fix missing pubspec.lock

Author: yukibtc

.github/workflows/ci.yml

@@ -30,5 +30,8 @@ jobs:
       - name: Install Flutter
         uses: subosito/flutter-action@v2
 
+      - name: Get Flutter deps
+        run: flutter pub get
+
       - name: Check
         run: bash contrib/scripts/check-crate.sh