submission_package: Avoid dangling std::string_view within SetTicketKeys()

GetName() returns a std::string by value, not by reference, so after the
std::string_view is constructed, it's not well defined to actually
execute any member functions of std::string_view that attempt to access
the data, as the std::string has already been destroyed. Instead, we can
just use a std::string and erase the last four characters.