Tidy: ignore non-Markdown files when linting for the Unstable Book
Tidy: ignore non-Markdown files when linting for the Unstable Book

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