[ci] Improve GitHub macOS workflow environment variables and clang-tidy conflicts

[sitaowang1998]

Request

#1044 introduces environment variables LLVM_PREFIX, CC, CXX, AR and RANLIB through GITHUB_ENV to force the dependency libraries to be compiled with llvm@16's clang++ compiler instead of AppleClang compiler, so we can use C++ 20 features in dependency libraries, e.g. ystdlib, that are not supported by old version of AppleClang on some macOS platforms.

Even though we set these environment variables, dependency libraries and clp are still compiled using macOS sdk standard libraries so that they are compatible with libraries installed through homebrew. However, these environment variables confuses clang-tidy, which now use llvm@16's standard libraries. The differences between two standard libraries cause clang-tidy to fail.

#1044 uses a temporary solution to "unset" the environment variables, but we need to find a better solution.

Possible implementation

Need further exploration.