Update GHA actions/cache to v4. Previous was deprecated

Author: bladecoder

.github/workflows/build.yml

@@ -13,7 +13,7 @@ jobs:
         with:
           java-version: 1.8
       - name: Cache Gradle packages
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: |
             ~/.gradle/caches