chore(deps): update actions/checkout action to v3 (#18)

Co-authored-by: Renovate Bot <[email protected]>

Author: renovate[bot]

.github/workflows/flutter-test.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
 
       - uses: subosito/[email protected]
         with: