Rollup merge of #33720 - mark-summerfield:patch-1, r=steveklabnik
Rollup merge of #33720 - mark-summerfield:patch-1, r=steveklabnik

Clarified that `let(mut x, y) =` only makes x mutable, not y

Closes #33716

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