Deserialization of tuples does not work on g++11

[mspertus]

It looks like tuple deserialization runs in a decltype(auto) bug in g++-11 as shown in this godbolt based on alpaca::detail::get.

A workaround seems to be to change the return type of alpaca::detail::get from decltype(auto) to auto & and change the bare return statements (that should never be call) to return a dummy int &. While ugly, since Since g++-11 is installed by default on Ubuntu 22.04 this is probably worth putting in the workaround.