Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/json.yml

@@ -7,7 +7,7 @@ jobs:
   test-json:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: json-syntax-check
         uses: limitusus/json-syntax-check@v2
         with:

.github/workflows/release.yml

@@ -10,7 +10,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Set up JDK 8
         uses: actions/setup-java@v5
         with:

.github/workflows/spellcheck.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out code.
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Check spelling
         uses: codespell-project/actions-codespell@v2
         with: