Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
     timeout-minutes: 15
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@1af3b93b6815bc44a9784bd300feb67ff0d1eeb3 # v6
     - name: Set up JDK 17
       uses: actions/setup-java@v4
       with: