chore(deps): update actions/checkout action to v4 (#109)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/flutter.yml

@@ -15,7 +15,7 @@ jobs:
         flutter-channel: [ 'stable' ]
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - uses: actions/setup-java@v4
         with: