CI: enable tests back for CMake builds

Author: robUx4

.github/workflows/cmake-multi-platform.yml

@@ -61,6 +61,7 @@ jobs:
         -DCMAKE_CXX_COMPILER=${{ matrix.cpp_compiler }}
         -DCMAKE_C_COMPILER=${{ matrix.c_compiler }}
         -DCMAKE_BUILD_TYPE=${{ matrix.build_type }}
+        -DBUILD_TESTING:BOOL=ON
         -S ${{ github.workspace }}
 
     - name: Build