`async_accept()` type deduction failure in C++20

[WolleTD]

When using async_accept(endpoint &, Token &&) with a generic lambda using auto for the second parameter and building as C++20, the type of the accepted socket is deduced to basic_stream_socket<ip::tcp, ip::tcp::endpoint>, using ip::tcp::endpoint as Executor, which obviously is wrong.

It works fine when building as C++17 or, obviously, when defining the type to ip::tcp::socket.

Minimal example:

#include <boost/asio.hpp>

using namespace boost::asio;

struct my_client {
    ip::tcp::socket socket;
};

int main(){
    io_context ctx;
    ip::tcp::acceptor acceptor(ctx, {{}, 6000});
    ip::tcp::endpoint peer_addr;

    // This compiles with -std=c++17, but fails with -std=c++20.
    // It works with c++20 when defining the type of `peer` as ip::tcp::socket.
    // auto derives to basic_stream_socket<ip::tcp, ip::tcp::endpoint> for
    // some reason.
    acceptor.async_accept(peer_addr, [](auto ec, auto peer) {
        auto client = my_client{std::move(peer)};
    });

    ctx.run();
}

Godbolt (with boost 1.81, but I tested locally with asio 1.27 – same issue)