Auto merge of #31806 - gokhanettin:to_lowercase-doc, r=japaric
Auto merge of #31806 - gokhanettin:to_lowercase-doc, r=japaric

`to_lowercase` example mistakenly calls `to_uppercase` function. This fixes the example.

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