COMP: slicerFunctionAddPythonQtResources - Fix unknown argument warning

Use COPYONLY instead of COPY_ONLY.

This commit fixes the following warning (caught by CMake 3.2.1):

//-------------------------
CMake Warning (dev) at CMake/SlicerFunctionAddPythonQtResources.cmake:34 (configure_file):
configure_file called with unknown argument(s):

COPY_ONLY

Call Stack (most recent call first):
Modules/Scripted/ExtensionWizard/CMakeLists.txt:18 (slicerFunctionAddPythonQtResources)
//-------------------------

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24123 3bd1e089-480b-0410-8dfb-8563597acbee