[clang-tools-extra] [clang-tidy] fix `bugprone-narrowing-conversions` false positive for conditional expression (PR #139474)

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AndreyG wrote:

Done. I've added tests for `short` and `int` and the same for C++. Also I noticed that in `trunk` there is the same issue in C++ for `short` (but not for `char`): https://github.com/llvm/llvm-project/issues/139467#issuecomment-3068027828. In my branch it's fixed.

https://github.com/llvm/llvm-project/pull/139474