At least for shiboken2 v5.13.0, cmake file set target Shiboken2::shiboken2, not variable SHIBOKEN_BINARY any more.
In shiboken_helper.cmake, we should detect and then choose to use ${SHIBOKEN_BINARY} or Shiboken2::shiboken2 correspondingly.
Workaround for users with this issue: change ${SHIBOKEN_BINARY} to Shiboken2::shiboken2 in shiboken_helper.cmake.