fix a compilation error detected locally by CTest

Number_types/test/Number_types/known_bit_size_integers.cpp

@@ -1,10 +1,10 @@
 #include <iostream>
-#include <boost/cstdint.hpp>
+#include <cstdint>
 #include <CGAL/assertions.h>
 
 int main()
 {
-  std::cout << "Verifying the sizes of boost::[u]int{8,16,32,64}_t"
+  std::cout << "Verifying the sizes of std::[u]int{8,16,32,64}_t"
             << std::endl;
 
   static_assert(sizeof(std::int8_t)  == 1);