CI: upgrade actions/cache from v2 to v4

GitHub now auto-fails workflows using deprecated actions/cache v1/v2.
The existing actions: write permission already satisfies cache v4 requirements.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: 2 people

.github/workflows/android.yml

@@ -23,7 +23,7 @@ jobs:
           java-version: 17
 
       - name: Cache Gradle and wrapper
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: |
             ~/.gradle/caches