Fix DUAL_X_CARRIAGE endstops

\#8170 fixed

Marlin/src/module/endstops.cpp

           #endif
           test_dual_x_endstops(X_MAX, X2_MAX);
         #else
-          if (X_MIN_TEST) UPDATE_ENDSTOP(X, MAX);
+          if (X_MAX_TEST) UPDATE_ENDSTOP(X, MAX);
         #endif
 
       #endif