* 🔧 use proper GCC binary
* 🔧 add more GCC warning flags
* ⚗️ try fix from https://github.com/nlohmann/json/issues/3138#issuecomment-1015562666
* Fix custom allocator test build failures (C++20)
Allocator tests fail to compile in C++20 mode with clang+MS STL due
to missing copy constructors.
* Fix test build failures due to missing noexcept (gcc-12)
* alt_string has multiple member functions that should be marked noexcept.
* nlohmann::ordered_map constructors can be noexcept.
Compilation failures result from the warning flag -Werror=noexcept and
gcc-12.
* Disable broken comparison tests in C++20 mode
Co-authored-by: Niels Lohmann <mail@nlohmann.me>
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