Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
       - uses: actions/setup-java@v5
@@ -24,7 +24,7 @@ jobs:
     if: ${{ github.ref == 'refs/heads/main' || startswith(github.ref, 'refs/tags/') }}
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
       - uses: actions/setup-java@v5