[clang-tools-extra] [clang-tidy] fix cppcoreguidelines-narrowing-conversions false positives when narrowing integer to signed integer in C++20 (PR #116591)

[Congcong Cai via cfe-commits]

HerrCai0907 wrote:

I agree cppcoreguideline wants to check it. but since we have already allow the to unsigned cast later according to [conv.intergral] before c++20, I think here the behavior should be the same. we should either remove or accept both limitation.

https://github.com/llvm/llvm-project/pull/116591