Add custom command to configure dune-py after install_python.

cmake/modules/DunePythonInstallPackage.cmake

@@ -125,15 +125,19 @@ function(dune_python_install_package)
   # Determine a target name for installing this package
   string(REPLACE "/" "_" targetname "install_python_${CMAKE_CURRENT_SOURCE_DIR}_${PYINST_PATH}")
 
-  set(CONFIGURE_DUNEPY -m dune configure)
-
   # Add a custom target that globally installs this package if requested
   add_custom_target(${targetname}
                     COMMAND ${Python3_EXECUTABLE} ${INSTALL_CMDLINE}
-                    COMMAND ${Python3_EXECUTABLE} ${CONFIGURE_DUNEPY}
                     COMMENT "Installing the python package at ${PYINST_FULLPATH}"
                     )
 
+  # Add a custom command that triggers the configuration of dune-py
+  set(CONFIGURE_DUNEPY -m dune configure)
+
+  add_custom_command(TARGET ${targetname} POST_BUILD
+                     COMMAND ${Python3_EXECUTABLE} ${CONFIGURE_DUNEPY}
+                     )
+
   add_dependencies(install_python ${targetname})
 
   # Define rules for `make install` that install a wheel into a central wheelhouse