Fix 'G29 K' value

Marlin/src/feature/bedlevel/ubl/ubl_G29.cpp

     // use cases for the users. So we can wait and see what to do with it.
     //
 
-    if (parser.seen_test('K')) // Kompare Current Mesh Data to Specified Stored Mesh
+    if (parser.seen('K')) // Kompare Current Mesh Data to Specified Stored Mesh
       g29_compare_current_mesh_to_stored_mesh();
 
   #endif // UBL_DEVEL_DEBUGGING