ci: remove incorrect flag from ubuntu job

Author: sevenbunu

.github/workflows/ubuntu.yml

@@ -36,7 +36,6 @@ jobs:
                 -DCMAKE_CXX_COMPILER=g++-${{ matrix.gcc }} \
                 -DCMAKE_C_COMPILER=gcc-${{ matrix.gcc }}   \
                 -DCMAKE_BUILD_TYPE=${{ env.config }}       \
-                -DCUBOOL_BUILD_TESTS=ON                    \
                 -DCUBOOL_WITH_CUDA=OFF                     \
                 -DCUBOOL_WITH_SEQUENTIAL=ON                \
                 -DCUBOOL_GRAPH_ENABLE_TESTING=ON