Update CMakeLists to correctly find pybind11 alias targets
Update CMakeLists to correctly find pybind11 alias targets

Add an additional TARGET check in the root cmake file to correctly find
the pybind11 alias targets.

xtensor-stack/xtensor-python,QuantStack/xtensor-python,xtensor-stack/xtensor-python,QuantStack/xtensor-python