Fix intermittently failing test

The 3 factory PRs created in the `before.do` loop would very occasionally have duplicate repo_name's due to `repo_name { Faker::Lorem.words.first }` in `factories.rb` not being guaranteed to be unique each time.

The easy solution was just to pass a repo_name in, as the other tests in this block do not depend on repo_name being different. I also changed the test so that it only creates one PR, as 3 isn't necessary to test the condition.