Auto merge of #53883 - RalfJung:miri-assert, r=oli-obk
Auto merge of #53883 - RalfJung:miri-assert, r=oli-obk

miri engine: make sure we do not copy unsized data

r? @oli-obk

GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,GBGamer/rust,graydon/rust,aidancully/rust,graydon/rust,GBGamer/rust,GBGamer/rust,graydon/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,GBGamer/rust