Fix a warning

src/utils/Messenger.hpp

@@ -62,7 +62,7 @@ class Messenger
   PASTIS_INLINE
   Array<DataType> allToAll(const Array<DataType>& sent_array) const
   {
-    Assert(sent_array.size() == m_size);
+    Assert(sent_array.size() == static_cast<size_t>(m_size));
     if constexpr(std::is_same<DataType, int>()) {
       Array<int> recv_array(m_size);
       return _allToAll(sent_array, recv_array);