Merge pull request #9277 from oysteinkrog/fix/DualX_Endstops

[2.0.x] Fix DUAL_X_CARRIAGE endstop tests

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