Joshua, I believe you are asking if you have a API breaking change on a branch in your GitHub and have the corresponding updates to the integration tests on a forked version of that API’s collection, can you configure your CI pipeline to use Newman and run the matching branches?
If so, in my experience, Postman does not support this. The Postman API does not expose the Postman branch name when querying collections. So even if you know the Postman branch you want to use with Newman, you won’t be able to programmatically get the collection uid. You can do some hacky things, like include a branch name in the collection description or include a collection uid in your repo. But even doing this, it would be hard to trigger a merge of the forked Postman collection in sequence with the merge of your GitHub branch.
My approach so far has been to avoid breaking API and test changes as much as possible. This allows for the master Postman collection to be updated and for CI to still function. When changes can’t be avoided, manually executing tests on a Postman branch and including evidence in the PR for reviewers (then merge the two branches manually at the same time). In the most extreme cases, we would need to block the CICD queue for that API to perform testings/merges.
My current approach is not sustainable or scalable. Hopefully, someone else has a real solution or Postman will provide better support for this. Anytime your tests and code are in different repos CICD gets much more complicated.