[clang] Fix a typo in webkit.NoUncountedMemberChecker. (PR #91402)

[Artem Dergachev via cfe-commits]

https://github.com/haoNoQ approved this pull request.

Nice LGTM!

You could test this patch by pasting the warning into one of the `expected-warning{{}}` clauses in the tests but I honestly don't think it's all that important for a patch like this.

https://github.com/llvm/llvm-project/pull/91402