Cannot open PR after PR already opened once.

[adong]

What happened: Using SD onboarding UI, we cannot create multiple PRs even if previous PRs were closed.

After raising a PR successfully

Close such PR, and delete this pipeline,

When onboard this repo again, we see errors

Failure API: https://api.screwdriver.cd/v4/pipelines/111222/openPr

Payload

What you expected to happen: Users should not see this error, regardless if they close PRs and/or deleting pipelines

How to reproduce it: see section in "what happened"