Remove hard error about C++11 requirement and update CI

include/boost/polymorphic_cast.hpp

@@ -49,18 +49,12 @@
 #ifndef BOOST_POLYMORPHIC_CAST_HPP
 #define BOOST_POLYMORPHIC_CAST_HPP
 
-#include <boost/config/assert_cxx11.hpp>
+#include <boost/config.hpp>
 
 #ifdef BOOST_HAS_PRAGMA_ONCE
 #   pragma once
 #endif
 
-
-#if defined(BOOST_NO_CXX11_HDR_TYPE_TRAITS)
-#error C++03 support is removed in Boost.Conversion 1.84
-#endif
-
-
 # include <boost/assert.hpp>
 # include <boost/throw_exception.hpp>