add_flag is ambiguous with c++20

[steffenb7333]

Code:

#include <CLI/CLI.hpp>

int main()
{
    auto app = CLI::App{"test"};
    auto flag = app.add_flag("--flag", "desc");
    return 0;
}

Compiling with
g++ -std=c++20 cli11.cpp

results in

cli11.cpp: In function 'int main()':
cli11.cpp:6:29: error: call of overloaded 'add_flag(const char [7], const char [5])' is ambiguous

CLI11 is version 2.1.2. g++ is 11.2.0.