Remove invalid dependency on FLATBUFFERS_GENERATE_HEADERS_SCHEMAS (google#8834)

* 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>

Author: nikolaseu

CMake/BuildFlatBuffers.cmake

@@ -305,8 +305,7 @@ function(flatbuffers_generate_headers)
       ${FLATBUFFERS_GENERATE_HEADERS_SCHEMAS})
   add_dependencies(
     ${FLATBUFFERS_GENERATE_HEADERS_TARGET}
-    ${FLATC}
-    ${FLATBUFFERS_GENERATE_HEADERS_SCHEMAS})
+    ${FLATC_TARGET})
   target_include_directories(
     ${FLATBUFFERS_GENERATE_HEADERS_TARGET}
     INTERFACE ${generated_target_dir})