[clang] [NFC][Clang] Fix enumerated mismatch warning (PR #112816)

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https://github.com/Sirraide requested changes to this pull request.

This doesn’t seem right: that diagnostic is only used in the parser, which is why it is in `DiagnosticParseKinds.td`. Instead, it’d be better to cast the two diagnostic IDs that are causing the problem to `unsigned` where they’re used.

https://github.com/llvm/llvm-project/pull/112816