Renamed directory godot_headers to godot-headers in GDNative SConstruct (#4714)

Fixes GDNative compile error caused by directoy name change in godot-cpp repository.

tutorials/plugins/gdnative/files/cpp_example/SConstruct

@@ -15,7 +15,7 @@ opts.Add(PathVariable('target_path', 'The path where the lib is installed.', 'de
 opts.Add(PathVariable('target_name', 'The library name.', 'libgdexample', PathVariable.PathAccept))
 
 # Local dependency paths, adapt them to your setup
-godot_headers_path = "godot-cpp/godot_headers/"
+godot_headers_path = "godot-cpp/godot-headers/"
 cpp_bindings_path = "godot-cpp/"
 cpp_library = "libgodot-cpp"