Update actions/checkout action to v5

Author: renovate[bot]

.github/workflows/dart.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Clone repository
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       # Note: This workflow uses the latest stable version of the Dart SDK.
       # You can specify other versions if desired, see documentation here:
       # https://github.com/dart-lang/setup-dart/blob/main/README.md