install(EXPORT): Fall back to set_property(APPEND) for FILE_SET
FILE_SET was introduced in CMake 3.23, so install(EXPORT) puts it behind a version gate. However, this results in the include directories not being picked up by older versions of CMake. Fall back to set_property(APPEND) for versions of CMake older than 3.23.
Fixes: #24787 (closed)
Edited by Kyle Edwards