* Remove invalid dependency on FLATBUFFERS_GENERATE_HEADERS_SCHEMAS
add_dependencies() is for targets.
CMake 4.2.0 fails because of this (it shouldn't crash though, but that's another topic). See https://gitlab.kitware.com/cmake/cmake/-/issues/27415
* Use FLATC_TARGET
---------
Co-authored-by: Justin Davis <jtdavis777@gmail.com>