Since commit v3.10.0-rc1~391^2~3 (Add directory property 'LABELS' and
CMAKE_DIRECTORY_LABELS variable, 2017-06-23) this command was
accidentally not allowed in script mode. It was dropped because
`ctest -S` mode needs to start with CMake's normal script mode and
then replace the `set_directory_properties` implementation. Restore
the normal `set_directory_properties` in script mode and then add
special logic to replace it in ctest. Also add a test case.
Fixes: #18523
