Extend CI C++ build cache

The CI didn't cache the C++ build related directories under `app/build/` which caused a full recompilation of C++ code, this takes a significant amount of time.

.github/workflows/ci.yml

@@ -23,7 +23,9 @@ jobs:
       - name: Restore CXX Cache
         uses: actions/cache@v3
         with:
-          path: app/.cxx/
+          path: |
+            app/.cxx/
+            app/build/intermediates/cxx/
           key: ${{ runner.os }}-cxx-${{ hashFiles('**/CMakeLists.txt') }}
 
       - name: Install Ninja Build