[llvm] [Peephole] Check instructions from CopyMIs are still COPY (PR #69511)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

> @mstorsjo, @mikaelholmen, is it urgent for you to fix the assertion?

The failed assertion breaks some of my builds, and unless we have a fix soon I would suggest we revert the offending commit - which I believe is what our developer policy prescribes anyway.

https://github.com/llvm/llvm-project/pull/69511