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

Author: renovate[bot]

.github/workflows/build-docker-image.yaml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 10
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3

.github/workflows/lint-renovate.yaml

@@ -15,5 +15,5 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 3
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: suzuki-shunsuke/github-action-renovate-config-validator@v1.1.1