Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/maven.yml

@@ -12,11 +12,11 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Checkout code
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         path: code
     - name: Checkout pages
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         path: gh-pages
         ref: gh-pages