Explicitly allow cache-write for test invocations

The `gradle-build-action` test workflows need to write cache entries,
even when run on non-default branches. This change add explicit configuration
to set `cache-read-only: false` when cache writing is required.

.github/workflows/integ-test-action-inputs-caching.yml

@@ -31,6 +31,7 @@ jobs:
     - name: Setup Gradle
       uses: ./
       with:
+        cache-read-only: false # For testing, allow writing cache entries on non-default branches
         # Add "enterprise" to main cache entry but omit "notifications"
         gradle-home-cache-includes: |
             caches