Clear and generate new cache only when merging to develop (#2549)

Clearing the cache regularly doesn't work because on each new merge to develop a new cache of almost 4GB will be created and replace the 'cleared' one.

We can try doing a clean up to this cache we're about to save so it's a bit smaller.

.github/workflows/tests.yml

@@ -47,6 +47,7 @@ jobs:
         uses: gradle/actions/setup-gradle@v3
         with:
           cache-read-only: ${{ github.ref != 'refs/heads/develop' }}
+          gradle-home-cache-cleanup: ${{ github.ref == 'refs/heads/develop' }}
 
       - name: ⚙️ Run unit tests, debug and release
         run: ./gradlew test $CI_GRADLE_ARG_PROPERTIES