Fix UNKNOWN_Z_NO_RAISE in G28

Bug introduced in 73fc0778b8

Marlin/src/gcode/calibrate/G28.cpp

@@ -312,7 +312,7 @@ void GcodeSuite::G28() {
     #endif
 
     const float z_homing_height =
-      ENABLED(UNKNOWN_Z_NO_RAISE) && TEST(axis_known_position, Z_AXIS)
+      ENABLED(UNKNOWN_Z_NO_RAISE) && !TEST(axis_known_position, Z_AXIS)
         ? 0
         : (parser.seenval('R') ? parser.value_linear_units() : Z_HOMING_HEIGHT);