[cmake] do not add python modules to all target

cmake/modules/DunePybindxiUtils.cmake

@@ -12,7 +12,7 @@
 # dune_pybindxi_add_module(<name> source1 [source2 ...])
 #
 function(dune_pybindxi_add_module target_name)
-  add_library(${target_name} MODULE ${ARGN})
+  add_library(${target_name} MODULE EXCLUDE_FROM_ALL ${ARGN})
   target_include_directories(${target_name}
     PRIVATE ${PYBIND11_INCLUDE_DIR}
     PRIVATE ${PYTHON_INCLUDE_DIRS})