💚 update actions/checkout to v3

Author: okaryo

.github/workflows/test-and-lint.yml

@@ -26,7 +26,7 @@ jobs:
     name: Run lint
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
     - name: Set up Flutter
       uses: subosito/flutter-action@v2
       with: