ci: encrypted gradle cache

Author: iseki0

.github/workflows/build.yml

@@ -23,6 +23,7 @@ jobs:
       - name: Set up Gradle
         uses: gradle/actions/setup-gradle@v3
         with:
+          cache-encryption-key: ${{ secrets.GradleEncryptionKey }}
           validate-wrappers: true
           build-scan-publish: true
           build-scan-terms-of-use-url: "https://gradle.com/terms-of-service"