message: turn off the backend in gh-page job
diff: @@ -875,7 +875,8 @@ gh-pages:
  -DCMAKE_CUDA_COMPILER=${CUDA_COMPILER} -DCMAKE_BUILD_TYPE=${BUILD_TYPE}
  -DBUILD_SHARED_LIBS=ON ${EXTRA_CMAKE_FLAGS} -DGINKGO_DEVEL_TOOLS=OFF
  -DGINKGO_BUILD_REFERENCE=OFF -DGINKGO_BUILD_OMP=OFF -DGINKGO_BUILD_CUDA=OFF
  - -DGINKGO_BUILD_HIP=OFF -DGINKGO_BUILD_TESTS=OFF -DGINKGO_BUILD_EXAMPLES=OFF
  + -DGINKGO_BUILD_HIP=OFF -DGINKGO_BUILD_DPCPP=OFF -DGINKGO_BUILD_MPI=OFF
  + -DGINKGO_BUILD_TESTS=OFF -DGINKGO_BUILD_EXAMPLES=OFF
  -DGINKGO_BUILD_DOC=ON -DGINKGO_DOC_GENERATE_PDF=ON
  - make usr
  - make pdf
  