Change badge branch master -> auto
Change badge branch master -> auto

For some reason GHA classifies the bors merges on the master branch as a
push to the auto branch, even though the workflow got triggered by a
push to the master branch. I guess this has something to do with the
same commit hash on master+auto directly after the merge?

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