dependency: Update actions/cache action to v6

Author: renovate[bot]

.github/workflows/gradle.yml

@@ -18,7 +18,7 @@ jobs:
           distribution: temurin
           java-version: '21'
       - name: Cache Gradle
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         with:
           path: ~/.gradle/caches
           key: >-