🐛 Define 'HEAD' axes for Markforged

Fixes #22167

Marlin/src/core/types.h

@@ -83,7 +83,7 @@ enum AxisEnum : uint8_t {
   #undef _EN_ITEM
 
   // Core also keeps toolhead directions
-  #if IS_CORE
+  #if EITHER(IS_CORE, MARKFORGED_XY)
     , X_HEAD, Y_HEAD, Z_HEAD
   #endif