dependency: Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/gradle.yml

@@ -16,7 +16,7 @@ jobs:
       fail-fast: false
     steps:
       - name: Checkout
-        uses: actions/checkout@v4.3.1
+        uses: actions/checkout@v6.0.2
       - name: 'Set up JDK ${{ matrix.java }}'
         uses: actions/setup-java@v4.8.0
         with: