eliminate some warnings about range-based for loops incorrectly using references

tests/core/GridGeneratorTest.cpp

@@ -98,7 +98,7 @@ void rangeBasedTest()
    auto dx = Vector3<real_t>( Grid::iterator::getUnitCellX(spacing), Grid::iterator::getUnitCellY(spacing), Grid::iterator::getUnitCellZ(spacing) );
    auto lowerIt  = typename Grid::iterator(domain, Vector3<real_t>(5,5,5) - dx * 30, spacing);
    auto endIt = typename Grid::iterator();
-   for ( const auto& pt : Grid(domain, Vector3<real_t>(5,5,5) - dx * 30, spacing) )
+   for ( const auto pt : Grid(domain, Vector3<real_t>(5,5,5) - dx * 30, spacing) )
    {
       WALBERLA_CHECK( lowerIt != endIt );
       WALBERLA_CHECK_FLOAT_EQUAL( *lowerIt, pt);

tests/geometry/BinaryRawFileTest.cpp

@@ -59,7 +59,7 @@ void test( const std::string & filename, const Vector3<uint_t> & size, const std
       
       CellInterval ci( 0, 0, 0, cell_idx_c( size[0] ) - 1, cell_idx_c( size[1] ) - 1, cell_idx_c( size[2] ) - 1 );
 
-      for (const Cell & c : ci)
+      for (const Cell c : ci)
       {
          field->get( c ) = brf.get( uint_c( c[0] ), uint_c( c[1] ), uint_c( c[2] ) );
       }
@@ -100,7 +100,7 @@ void testScaled( const std::string & filename, const Vector3<uint_t> & size, con
 
       CellInterval ci( 0, 0, 0, cell_idx_c( scaledSize[0] ) - 1, cell_idx_c( scaledSize[1] ) - 1, cell_idx_c( scaledSize[2] ) - 1 );
 
-      for (const Cell & c : ci)
+      for (const Cell c : ci)
       {
          auto pos = blocks->getBlockLocalCellCenter( block, c );
          field->get( c ) = brfi.get( pos );