docker.test.yml: Checkout origin/master
docker.test.yml: Checkout origin/master

test-bot will build a bottle of the formula changed in the head commit
of the pull request.

Linuxbrew/brew,maxim-belkin/brew,hanxue/linuxbrew,Linuxbrew/brew,Linuxbrew/brew,hanxue/linuxbrew,rwhogg/brew,rwhogg/brew,maxim-belkin/brew,Linuxbrew/brew,maxim-belkin/brew,hanxue/linuxbrew,rwhogg/brew