Rollup merge of #63260 - RalfJung:ptr-test, r=matklad
Rollup merge of #63260 - RalfJung:ptr-test, r=matklad

fix UB in a test

We used to compare two mutable references that were supposed to point to the same thing. That's no good.

Compare them as raw pointers instead.

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