chore(deps): update actions/checkout action to v6 (#29)

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

Author: renovate[bot]

.github/workflows/tflint.yaml

@@ -14,7 +14,7 @@ jobs:
         os: [ubuntu-latest]
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         name: Checkout source code
 
       - uses: actions/cache@v4