[clang] [clang] When checking for covariant return types, make sure the poiners or references are to *classes* (PR #111856)

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https://github.com/Sirraide commented:

Implementation seems fine, but this is still missing a release note (in `clang/docs/ReleaseNotes.rst`, probably somewhere in the ‘Potentially Breaking Changes’ section).

CC @AaronBallman @cor3ntin Do we want to make this a warning that defaults to an error instead? Imo it’s probably fine as-is because I don’t imagine too many people would write code that abuses us not diagnosing this...

https://github.com/llvm/llvm-project/pull/111856