Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/build.yml

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