Investigate `create_pull_request` failing silently

[mokagio]

This build passed but no PR was created.

[AliSoftware]

FYI: From a quick look at the fastlane source code, seems like the CreatePullRequestAction is implemented in such a way that it will return the PR url when successful… and [nil in case of errors] (as opposed to exiting with non-zero).

Which means it's assumed that one is supposed to check the return value of create_pull_request to check if it succeeded or not.