[clang] [Clang] Fix FixIt for implicit-int diagnostics. (PR #179356)

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Sirraide wrote:

> I think the recent changes mean that the release notes need to be updated again. Also, this has outgrown the issue that is referenced there. I'll leave it up to you on how you see fit to handle this, I'm pretty content with it now.

I think the release note is fine as-is; we don’t need to mention every last detail in it

https://github.com/llvm/llvm-project/pull/179356