list pull requests bug with repo forked within an organisation

[stubduffy]

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Bug

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When using the list pull requests rest endpoint against a forked repo (within an organisation), and filtering by 'head', i seem not to be able to get any results and always just an empty list returned.

Reproduction Steps

• fork an organisation repo myorg/repo => myorg/forked-repo
• create a PR on the fork, e.g. from branch name mybranch
• call list pull requests on the forked repo, filtering by the head param head=myorg%3Amybranch

This was found whilst trying to debug a problem with a bot checking for updates which tries to create PRs, which was failing to find those already existing and subsequently encountering an error when trying to create new.

I did a fair amount of playing with scenarios, and it seemed to only be an issue if the fork was within an organisation. It worked fine for forks to a personal account.

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