🐛 Fix M423 invocation (#24360)

Followup to #23745

Marlin/src/gcode/gcode.cpp

         case 421: M421(); break;                                  // M421: Set a Mesh Bed Leveling Z coordinate
       #endif
 
+      #if ENABLED(X_AXIS_TWIST_COMPENSATION)
+        case 423: M423(); break;                                  // M423: Reset, modify, or report X-Twist Compensation data
+      #endif
+
       #if ENABLED(BACKLASH_GCODE)
         case 425: M425(); break;                                  // M425: Tune backlash compensation
       #endif