We have a regression regarding management of types convertible to 
value_type. It is an occurrence of PR 56112 but for the insert method.

     libstdc++: [_Hashtable] Insert range of types convertible to 
value_type PR 56112

     Fix insertion of range of types convertible to value_type.

     libstdc++-v3/ChangeLog:

             PR libstdc++/56112
             * include/bits/hashtable.h
             (_Hashtable<>::_M_insert_unique_aux): New.
             (_Hashtable<>::_S_to_value): New.
             (_Hashtable<>::_M_insert(_Arg&&, const _NodeGenerator&, 
true_type)): Use latters.
             * testsuite/23_containers/unordered_map/cons/56112.cc: Use 
dg-do compile.
             * testsuite/23_containers/unordered_set/cons/56112.cc: New 
test.

Tested under Linux x86_64.

Ok to commit ?

François