Update actions/cache action to v6

Author: renovate[bot]

.github/workflows/android.yml

@@ -48,7 +48,7 @@ jobs:
           java-version: 21
 
       - name: Cache Gradle and wrapper
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         with:
           path: |
             ~/.gradle/caches

.github/workflows/publish-docs.yml

@@ -16,7 +16,7 @@ jobs:
         with:
           python-version: 3.x
       - run: echo "cache_id=$(date --utc '+%V')" >> $GITHUB_ENV 
-      - uses: actions/cache@v5
+      - uses: actions/cache@v6
         with:
           key: mkdocs-material-${{ env.cache_id }}
           path: .cache