needless_doctest_main: False positive for async fn
needless_doctest_main: False positive for async fn

Fixes #5188.

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