Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/maven.yml

@@ -17,7 +17,7 @@ jobs:
     steps:
     - run: |
         sudo apt-get install xmlstarlet -yq
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Set up JDK 17
       uses: actions/setup-java@v4
       with: