Update gradle/actions action to v6

Author: renovate[bot]

.github/workflows/validation.yml

@@ -34,7 +34,7 @@ jobs:
           distribution: temurin
           java-version: 21
 
-      - uses: gradle/actions/setup-gradle@v5
+      - uses: gradle/actions/setup-gradle@v6
         with:
           cache-disabled: true