Rollup merge of #35878 - matthew-piziak:ptr-assertions, r=GuillaumeGomez
Rollup merge of #35878 - matthew-piziak:ptr-assertions, r=GuillaumeGomez

replace `println!` statements with `assert!`ions in `std::ptr` examples

r? @steveklabnik

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