chore(deps): update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/gradle-build.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Setup Java
         uses: actions/setup-java@v5