dependency: Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/gradle.yml

@@ -15,7 +15,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Set up JDK 17
         uses: actions/setup-java@v5
         with: