Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/gradle.yml

@@ -12,7 +12,7 @@ jobs:
     timeout-minutes: 30
 
     steps:
-    - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5
+    - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
 
     - name: Set up JDK 17
       uses: actions/setup-java@dded0888837ed1f317902acf8a20df0ad188d165 # v5