Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/gradle.yml

@@ -14,7 +14,7 @@ jobs:
       contents: read
 
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - name: Set up JDK 17
       uses: actions/setup-java@v5
       with:
@@ -36,7 +36,7 @@ jobs:
       contents: write
 
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - name: Set up JDK 17
       uses: actions/setup-java@v5
       with: