Update GitHub Actions workflow to use actions/cache@v4

The workflow was using the deprecated actions/cache@v2 which GitHub
is now automatically failing. Updated to v4 to fix CI build failures.

Co-Authored-By: Sam Fertig <sam.fertig@codeium.com>

Author: devin-ai-integration[bot]

.github/workflows/gradle.yml

@@ -22,7 +22,7 @@ jobs:
       with:
         distribution: zulu
         java-version: '11'
-    - uses: actions/cache@v2
+    - uses: actions/cache@v4
       with:
         path: |
           ~/.gradle/caches