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

Author: renovate[bot]

.github/workflows/actionlint.yaml

@@ -11,7 +11,7 @@ jobs:
     name: actionlint with reviewdog
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: actionlint
         uses: reviewdog/action-actionlint@v1
         with:

.github/workflows/ci.yaml

@@ -7,7 +7,7 @@ jobs:
   build-gradle-project:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: "true"
       - uses: actions/setup-java@v4

.github/workflows/report.yaml

@@ -16,7 +16,7 @@ jobs:
       pages: write
       id-token: write
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: xu-cheng/latex-action@v3
         with:
           root_file: report.tex