[clang] [clang][Sema] Add regression test for invalid friend declaration (PR #224798)

[Mariya Podchishchaeva via cfe-commits]

Fznamznon wrote:

@JeewoongKim , could you please tweak PR desc a bit, this is important because this turns into commit message that will show up in history. Please remove "tested locally" as it is not useful information for history, and I think this PR will close the linked issue, so please use Fixes <issue link> syntax so it happens automatically. These are useful practices you can apply to your further PRs. When done, please poke me with a tag and I'll merge it for you.

https://github.com/llvm/llvm-project/pull/224798