[clang-tools-extra] Fix false positive in bugprone-throw-keyword-missing (PR #115302)

[Julian Schmidt via cfe-commits]

https://github.com/5chmidti approved this pull request.

LGTM

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I filed #115540 because I noticed how the `hasAncestor` matcher in the `unless` part means that we are excluding quite some cases. (unrelated to this PRI)

https://github.com/llvm/llvm-project/pull/115302