[clang-tools-extra] [clang-tidy] Fix false positives in `bugprone-signed-char-misuse` (PR #149790)

[Björn Svensson via cfe-commits]

bjosv wrote:

Hum, the release notes seems to have been cleared again, and I think there are some entries lost.
I now see that some of the release notes are recovered so I'll rebase when main is stable again.

https://github.com/llvm/llvm-project/pull/149790