tidy: make a field private rather than protected

alib2graph_data/src/grid/square/WeightedSquareGrid8.hpp

@@ -20,7 +20,7 @@ class WeightedSquareGrid8 final : public SquareGrid<TCoordinate, TEdge> {
   using direction_type = SquareGridDirections;
 // ---------------------------------------------------------------------------------------------------------------------
- protected:
+ private:
   typename edge_type::weight_type m_unit;
 // =====================================================================================================================