docs: Update rustc_middle::middle::region::ScopeTree
docs: Update rustc_middle::middle::region::ScopeTree

This corrects the return type in docs for yield_in_source method.

Closes #80287.

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