[llvm] [ML Inliner] Fix inconsistancy between CallGraph and FunctionLevels (PR #122830)

[Peter Rong via llvm-commits]

DataCorrupted wrote:

> How difficult is it to construct a regression test for this?

I'm happy to, but I've spent a few hours trying to create one with no luck. I don't have enough understanding of co_await nor CG to understand the root cause of the inconsistency. Any hints?

https://github.com/llvm/llvm-project/pull/122830