[clang] Fix false negative when value initializing a field annotated with [[clang::require_field_initialization]] (PR #124329)

[via cfe-commits]

llvmbot wrote:

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>> this would need to be backported (https://releases.llvm.org/19.1.0/docs/GitHub.html#backporting-fixes-to-the-release-branches).
>
>Oh, @AaronBallman - would you mind adding this as a milestone so I can `/cherry-pick` here?

Error: Command failed due to missing milestone.

https://github.com/llvm/llvm-project/pull/124329