deps: update actions/checkout action to v6

Author: renovate-bot

.github/workflows/unmanaged_dependency_check.yaml

@@ -5,7 +5,7 @@ jobs:
   unmanaged_dependency_check:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - uses: actions/setup-java@v4
       with:
         distribution: temurin