[clang-tidy] Fix false positives on C23 enums in `bugprone-signed-char-misuse` (#149790)
Ignore false positives on C23 enums which allows setting the fixed
underlying type to signed char.
The AST tree for C enums includes a ImplicitCastExp
(that was matched) but this is not the case for C++ enums.
Fixes #145651
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Signed-off-by: Björn Svensson <bjorn.a.svensson@est.tech>