Disable leveling during G12 (#14385)

Marlin/src/gcode/feature/clean/G12.cpp

 #include "../../parser.h"
 #include "../../../module/motion.h"
 
+#if HAS_LEVELING
+  #include "../../../module/planner.h"
+  #include "../../../feature/bedlevel/bedlevel.h"
+#endif
+
 /**
  * G12: Clean the nozzle
  */
                 objects = parser.ushortval('T', NOZZLE_CLEAN_TRIANGLES);
   const float radius = parser.floatval('R', NOZZLE_CLEAN_CIRCLE_RADIUS);
 
+  #if HAS_LEVELING
+    const bool was_enabled = planner.leveling_active;
+    set_bed_leveling_enabled(false);
+  #endif
+
   Nozzle::clean(pattern, strokes, radius, objects);
+
+  // Re-enable bed level correction if it had been on
+  #if HAS_LEVELING
+    set_bed_leveling_enabled(was_enabled);
+  #endif
 }
 
 #endif // NOZZLE_CLEAN_FEATURE